Let's begin at the beginning. Why is gasoline oxygenated, that is, additives such as ethanol added to it bearing oxygen chemically? One word: Emissions. Fuel oxygenates first and foremost constitute a sort of passive emissions control program. They do something a little "Big-Brotherish": they unilaterally force early model vehicles to comply with much later model emissions standards, standards they were never designed to meet. These (innocent, unsuspecting) vehicles are the sole target. Later, more modern computer-controlled vehicles aren't affected. But the older, target vehicles lean out slightly in the presence of ethanol gas, improving exhaust emissions. But doesn't this affect performance? No. Because manufacturers build into every vehicle something quite interesting: a margin of over-richness for driveability and reliability. The driveability concerns different sales destinations, the reliability a hedge in terms of warranty. This of course includes motorcycles. Every streetable motor vehicle has this margin. Ethanol, MTBE, and other oxygenates take advantage of, manipulate, capitalize on, this rich margin for emissions purposes, by targetting it and very carefully and very slightly reducing it for the emissions-control goal. The manufacturers put that margin in there, the government preempts and tweaks it to their advantage. The result is as intended: reduced exhaust emissions with no bad effects. That's the *why* and the *how* of ethanol.

Note that I said, "no bad effects." Ethanol is not the evil scourge media says it is. That's a fairy tale. The American Motorcyclist Association (AMA), in its usual style and arguably what it's best at, is perpetuating a myth. Just as with the scare-mongering the AMA engaged in during the 1980s concerning tetra-ethel-lead, today they are similarly popularizing the notion that oxygenated gasoline is harmful to powersports vehicles. And the rest of media has run with the ball. And how! But let's put on the brakes. Let's look at this fallacy in terms of its three most insidious claims: corrosion, loss of performance, and chemical damage of rubber components. Plus, we'll visit a fourth, related misconception regarding ethanol and modern gasoline's very short shelf life. Here we go.

First, corrosion. The idea that oxygenated gasoline corrodes carburetors started in the marine world, and it is in fact the National Marine Manufacturers Association (NMMA) that began all the current hoopla by lobbying the government concerning ethanol gas. Subsequent to the NMMA's involvement, the AMA joined the controversy. The simple fact is, marine carburetors, where and when they still exist, have (had) bimetallic construction, that is, steel float bowls bolted to low grade aluminum carb bodies -- a dissimilar metals combination that is a sure recipe for electrolysis-generated corrosion, especially when combined with a life near water. You find this same bimetal construction on your lawn mower and portable generator, by the way. But not on any motorcycle made in the last 80 years. Certainly, the presence of moisture is going to wreak havoc on this kind of carburetor, and I don't fault the marine industry for its concern. Of course, with fuel injection this has become moot, but I think the marine industry would better have served its customers by long ago bringing its fuel systems into the modern era. And since stationary engines use the very same carburetors, maybe those manufacturers should be advocating alongside the NMMA. But guess what, they aren't.

An unfortunate corrollary to this is that the motorcycle industry for a long time made their own version of very corrosion-prone carburetors. Up til around 1978 in fact. While not steel combined with aluminum like marine carbs, bike carbs were however at one time cast of a very low grade aluminum alloy heavy in zinc because this metal was easiest to manufacture. This high-zinc alloy made these carburetors very susceptible to corrosion. In worst cases they simply wear away before your eyes, slower or faster depending on the environment they live in. But it is incorrect to blame oxygenated fuel when these zinc carburetors corrode. They have always corroded more than other carburetors -- much more, and ethanol gas is not appreciably hastening that. No motorcycle, ATV, scooter, personal watercraft, snowmobile, or recreational vehicle's carburetor is more than slightly more at risk for corrosion due to ethanol than before there was ethanol, and post-1978 carbs never were vulnerable (by 1980 few manufacturers were still making zinc carbs -- Euro makers being the holdout).

Second, performance issues. Remember that richness margin oxygenated fuel targets and preempts? Normally, there is no harm in this. The factory-supplied margin, even reduced slightly (but not entirely) by ethanol, is enough to do the job it was intended to, when the engine is healthy. But that "if" is important, because you can't escape the fact that narrowing the margin does *potentially* put the engine a little bit at risk; placing the engine onto a steep precipice from which it can, under the right conditions, fall. And fall it does when maintenance is neglected; when there are tuning shortcomings. When that happens, when the engine is poorly cared for, the bike's fuel needs are then pushed deeper into the margin, a margin now reduced due to oxygenates, and performance can suffer. But this is all worse-case scenario. It's not even close to being a given, and more importantly, it is not the gasoline's fault. It's the bike's. Most motorcycles are badly maintained, and vintage bikes most of all. It's just a fact. Consider this: all of us on the inside of the industry (mechanics and other motorcycle "lifers") are using readily-available oxygenated pump gas without a second thought and without consequence. Ethanol gas is a concern in terms of performance only when the bike has low compression, dirty carburetors, neglected ignition components, and other maintenance shortcomings.

Third, the supposed deterioration of rubber parts. This one is simply a misunderstanding common among folks who have little or no history in the motorcycle field. There is a lot of crap out there masquerading as carburetor parts, kits and similar parts that no concientious mechanic would ever use. These parts do indeed fail to hold up. However, no high quality stock or aftermarket replacement rubber parts swell or break down any more than they did back in the 60s and 70s long before ethanol fuel was common. What, they do swell? Yes, even the OEM stuff. Ask any longtime career mechanic about the slight swelling of factory float bowl gaskets, not in use but when handled after being doused with gasoline. This is not a Viton versus buna rubber issue. Not at all. It's more a $3 carb gasket versus a 50-cent gasket issue. And it's always been that way.

Fourth and finally, there is the myth that oxygenates in the fuel cause it to break down and go bad faster. This is silly. It's inarguable that modern gas breaks down surprisingly quickly, much faster than it used to. However, as with so many things, the Internet "experts" have got this one backward too. It's not the oxygenates that make the fuel break down faster but rather the removal of the aromatics (benzene, toluene and xylene) that were common in gasoline fifty years ago that result in our fuel's short storage life. The aromatics are no longer there to preserve it. That's right. It's not what's *in* the gas but what's *not* in it that is the problem, when it comes to fuel deterioration.

Let's recap. First, carburetor corrosion has more to do with the quality of the carb's manufacture than with ethanol, though admittedly ethanol's moisture-attraction potential doesn't do these zinc carbs any favors. Second, performance issues do potentially exist due to ethanol but the plain truth is, they materialize only when combined with poor maintenance, and inadequate maintenance is endemic in the powersports world. Third, only the very poorest aftermarket rubber parts deteriorate in the presence of ethanol and occasional slight swelling of good quality gaskets during service operations is normal and to be expected whatever the fuel. And fourth, the powersports industry has recognized (and communicated) for many years now that modern gasoline gels (starts turning to varnish) in as quickly as three weeks, due to the removal of gasoline's aromatic ingredients in compliance with evaporative emissions regulations. Ethanol is not the reason for that. Dumbed-down gas is.

Those who perpetuate the "ethanol myth" don't understand the technology, don't know the history, and aren't aware of the forces at work in the powersports industry. It is not true that today's oxygenated fuels are demonstrably harmful to either carburetor durability or carburetor function. Good fuels and good people are being unjustly maligned due to this nonsense. It's time this myth was busted and reason was brought to bear.

There is a pervasive but false notion that your carburetor's throttle shaft seals contribute to performance issues. Actually, they don't. These felt rings are dust seals only, not vacuum seals. In other words, your carburetors have a designed-in amount of air leakage past the throttle shafts. This is normal and it's the way all Keihin and Mikuni CV carbs are, not just Gold Wing carbs. For this reason, though I sell the seals (all four sizes in fact), I am indifferent about their replacement. The sole job of the felt seals is to slow the entry of abrasive dirt that would hasten the wear of the brass bushings the throttle shafts are mounted in. That's it. They guard the bushings, not the vacuum.

There is a second misunderstanding associated with this one, and that is the idea that spraying flammable aerosol products on the carburetors can help detect vacuum leaks. Though like cat videos on YouTube this fallacy virtually defines motorcycle user forums, no thinking mechanic uses anything like that method to check for vacuum leaks. Here's why. A carburetor has half a dozen openings to atmosphere all around it. Any flammable substance sprayed even a short distance -- let alone right at -- the carburetor is going to be picked up by the carburetor and will then affect engine running. Doesn't tell you anything. A professional mechanic uses the historic less air test to find vacuum leaks.

A third tie-in to the subject of felt seals is the mistaken belief that chemical dip and other immersion methods of carburetor cleaning necessarily hurt the seals. Sure, felt seals deteriorate over time and become dried up and shrunken, in extreme cases to the point that removing them results in their basically flaking away into dusty bits on the workbench. But that's not the fault of dipping. That's entropy. Again, they're only dust seals, long-term guardians of the throttle shaft bearings.

Instead of all this hand-wringing over supposed effects the felt seals have on performance, it is much wiser to go after the things that really do hurt engine efficiency. There are several. The number one thing to eliminate as a performance problem on vintage Japanese bikes is low cylinder compression. See my articles on this. The fact is, the years do one big thing to these engines: makes 'em "out of breath". I tell all my customers they want 150 psi ("book" for most vibtage Hondas is 170), but unfortunately 120~140 is very common. It makes little sense to spend your energy on anything else -- ignition, carburetors, whatever-- if your engine develops less than 150 psi.

There is an astonishingly pervasive belief among motorcycle riders that the height of the carburetor's float is somehow linked to float bowl overflow. In other words, that a float's height is the carb's first defense against carburetor flooding. This is totally wacky. And worse, because it would then follow that an overflow condition could be corrected by float level adjustment. Not so. Yet this notion permeates the Internet. On my Youtube video showing how best to adjust floats, I get regular inquiries on how to adjust floats to stop overflow.

Overflow has many possible causes, however too high a float setting is at the very bottom of the list. The most common problem on many vintage bikes is cracked overflow standpipes, where they exist (they are absent in Wings). At least half of all the carbs I rebuild have to have their standpipes repaired. Next is poor bowl venting, whether due to blocked vent passages or improperly installed or routed vent hoses. And then of course there is the leaking float valve, whether due to debris, varnish, water, wear, modification, or simply poor quality valves. And that last is worthy of some thought. The Wing carburetor, in all its permutations, lacks an overflow indication system, meaning overflow is more serious than on other bikes because there is no visual that fuel is pouring into the cylinders. For that reason, if no other, using good float valves is critical, and there are no good valves except OEM.

Float level is equal to the volume knob on your radio. It regulates the height of fuel, which determines the amount of fuel accessible to all the carb's circuits. All of them. Controlling the richness or leanness of all. This is known by every career tech. So consider. Logic should first tell you that a float set to the manufacturer's spec can't possibly be the cause of overflow. Duh. Makes even less to change it anyway, as many do. Second, it is equally logical that if a carburetor were overflowing due to an excessively high float level, rich running would be a bigger problem than overflow. Your first concern would be to get off that slug and park it until you figured out why it runs like it's towing a motor home. Seriously. The bike would run so bad you would never even have *thought* of overflow.

Float level is all about calibration, not liquid tightness. Like the jets, slide dimensions and even the carb's bore size, the float level is one of the specifications predetermined by the carburetor maker to control air/fuel mixture. Period. Race tuners appreciate this, as they use float level in the same way they use jets, adjusting both to suit tuning needs, and even some of the bike manufacturers themselves have issued notices to alter float level to solve performance issues. Float level = mixture control. Nothing else. If you experience carburetor overflow, fix the problem. Don't try to strangle the carb dry by altering float level. Shutting off your house's water main isn't how you fix leaky plumbing.

But what if adjustment *is* warranted? Previous work has been inexpert, the adjustments have vibrated out of spec, whatever. It seems many have forgotten that before carburetors got so heavy, manufacturers used to consistently describe adjustment with the carburetor right-side-up, that is, in its normal position. It's still the preferred way in my view, no matter the carb type or vintage. Show me a float adjusted in any position other than right side up and I will show you one that is anywhere from one to three millimeters off. Also, many seem to think the exact point at which a float shuts off a mysterious, difficult to obtain goal. I'm not sure why this is. But I know done right-side-up much of the confusion goes away. Also, the spring-loaded pin on the float valve is merely a shock absorber that protects the valve and its seat from repeated impact. It has nothing to do with float level. Nor is it true that the float's bottom edge should be level with the carb casting. That's a an Internet myth, no matter how pervasive. There are many carbs, even most, whose correct setting is not parallel with the casting. Some above it, some below. Older Mikunis for example are almost all markedly below.

Float level is important. The main practical benefit aside from correct mixture is a wonderfully smooth idle. I see incorrect float levels every day. Most are minor, but many are so far off you have to wonder what went on the last time the carbs were worked on. A simple system, the carburetor float. But so widely misunderstood. Hopefully this exploration has put some light on the subject. Check out the aforementioned video at https://youtu.be/aiexehn33kg.

Forums and other Internet sources consistently endorse carburetor rebuild kits. That alone should tell you something about them. No professional carburetor rebuilder uses rebuild kits. Because they're junk.

Even before I retired from Kawsasaki corporate and took my part-time carburetor business full-time I tried using aftermarket float valves. They are uniformly bad. I began testing brand-new ones right out of the package with a Mityvac before installing them. The result was I had to throw at least half of them away. They wouldn't seal. I had to buy eight to get four that would seal. Sometimes ten. And then, more often than not, even the ones that sealed initially quit sealing after a short while. And if that didn't happen then the plating that is put on these crappy float valves would begin to peel, resulting in overflow. Or the valves would fit poorly, too small in diameter or too long, both causing issues. The first thing a carburetor customer looks for is fuel tightness. I'm going to send him carbs I *know* are going to leak? Hardly. I can't understand why anyone would use these parts, especially people who rebuild carburetors for others.

Most folks know I try to concentrate on just Hondas, both in engine rebuilding and carburetor work. One reason is I really favor these machines. In addition, I like rebuilding carburetors for machines I am the most familiar with. That is, I know 70s and 80s Hondas well. I know where their weak points are. And know in some cases they can be overcome with small carb changes. The second reason, and an important one, I concentrate on Honda carburetors is they are the only brand factory float valves can be got for now. Later Kawasakis used the same brand of carbs as Honda and the float valves mostly interchange so I do a lot of those Kawasaki carburetors too. But if I can't get factory float valves for a carb set I won't rebuild the carbs. I won't make excuses. This is why I don't do older Kawasakis, Yamahas and Suzukis. There are no float valves left for these. The factories ran out of them long ago.

Someday I know Honda and Kawasaki will also stop selling their float valves, and I'll have to either stop rebuilding carburetors or start using crap float valves and making excuses to my customers. But I don't want to do that. What a terrible thing to have to do.

But here is the question you need to ask yourself. Why aren't the rebuilders who use K&L and other float valves making such excuses? Why aren't their customers being warned that the carbs could overflow at any time? It's perplexing to me. Maybe most customers fail to maintain their carbs from one season to the next (many do), and thus they never realize the poor quality parts that are in there, chalking up eventual leaking issues to "it's time to rebuild them again." I know many customers have their carbs rebuilt each season, usually by a different rebuilder each time. And I know for a fact that many rebuilders don't use good float valves because they just don't care. The crappy aftermarket valves cost $5 and the good OEM ones eight to ten times as much. You can see their motivation. In fact if it weren't for the seasonal nature of motorcycling in most of the country, the aftermarket carb parts companies would be seen for what they are and they would go out of business. Of that I convinced.

These bad float valves are often found in rebuild kits. Some forums have actually examined kits, comparing those from several different manufacturers. I really appreciate the trouble that went into those comparisons. But here's something I have to say. Putting carb kits up for comparison is like having a farting contest. The problem is the subject is still a fart. There is nothing good about carb rebuild kits.

For the life of me I cannot figure out the average consumer's fascination with them. Maybe it's the influence of the car repair trade. I dunno. But I know this, people within the industry have avoided them for decades, using instead quality rebuild parts from legitimate sources, including Honda themselves. No reasonably competent carburetor rebuilder uses kits. They're extremely cheaply made, and more importantly, frequently result in that supreme tragedy, the ignorant tossing of perfectly good and very difficult to find OEM jet needles and needle jets. I deal with this issue almost weekly, having to inform my customers of the presence of Chinese or "high performance" metering parts in their carbs and the cost to replace them with OEM. The problem is OEM is pretty expensive because it's available only by buying whole carburetor sets. This is the state of working with 40 to 50 year old carburetors.

Carb kits are like McNuggets. Aggressive advertising has put both firmly on the radar and inextricably embedded into the culture, but inversely and perversely relative to their quality. What power, commerce! Beware.

Internet "experts" often promote such bizarre troubleshooting techniques as spraying aerosols around the intake manifolds, not realizing or even willing to believe that maybe that is not the way professional mechanics do things. In fact it is not.

I was helping someone troubleshoot their bike. We duct taped half the air filter surface. The bike revved much better with the duct tape. So, a carburetion problem, right? No, not necessarily. After making sure the carbs were clean, there was good fuel flow to them, the air filters sealed well and were unobstructed, and there was a seal at the manifolds, we turned to the ignition system and found that one of the bike's spark plugs was firing, not at its electrode but down inside the plug, partway down the insulator, at a crack in the insulator. A misfire in other words. The partly drained voltage weakened the spark.

Another time a customer called me for advice. His Honda VF500F wouldn't rev up. I suggested the same test, taping up half the air filter. He reported back that it worked and he quickly discovered the loose intake manifold clamps as a result.

This is called the less air test and it really works. Not only that, it is the professional way to not only discover vacuum leaks, but more importantly, to narrow down troubleshooting possiblities between mechanical, intake, and ignition.

As a career powersports tech and votech educator, I find it more than curious, even humorous, that user forums propagate a technique that has so little to do with proper tuning and which owes so much to exhaust emissions goals. One more instance of the media latching onto the trivial at the cost of the vital. Honda's idle drop procedure is not part of correct idle mixture screw adjustment.

The idle drop procedure is uniquely Honda's. It originated on their early cars, in the slightly more involved form of the propane enrichment procedure. In that procedure, the mechanic attached to the carburetor a bottle of propane and adjusted the idle mixture in this condition. After getting a perfect idle, he then removed the propane bottle and gave the car back to the customer with no additional carburetor adjustments. What was the outcome? Of course! The customer received his car with the carburetor on the lean side. An emissions deal. For good or bad. When writing the same thing in their bike manuals, Honda hit on the less expensive equivalent of the idle drop procedure. Same setting, same goal, and same outcome. The mix is optimized, then intentionally worsened a certain amount, in the name of emissions. Call this whatever you like, it is not tuning.

To be fair, perhaps many motorcycle owners find the idle drop procedure to be a more accessible method of adjusting their pilot screws than either doing it the traditional way by ear or by using an exhaust gas analyzer. I can accept that. I think it a little juvenile, but I guess it works for some. What gets my back up is forums all over regurgitating the procedure as if it's best practice, or even good practice. Nonsense.

It is often stated that when undoing a Dynojet kit, which carb rebuilders such as myself find ourselves doing often, the slides that Dynojet has you drill out need to be replaced because of it. Not so. This shows a lack of awareness of what those holes do. I have removed countless Dynojet kits and never had to do anything about the enlarged slide holes. They don't really do anything.

What Dynojet was trying to do with the slide hole enlargement was to make the slide lift faster. First, the desired effect was to make the CV carb act more like a mechanical slide carb. This would theoretically be useful on a racetrack where throttle position changes are huge and frequent, and average rpm many times higher than in street use. Useful because the CV is designed with a certain amount of lag between throttle plate opening and slide lift, and enlarging the pressure access holes, designed merely to get negative pressure above the diaphragm, promised to make that happen. However, and second, it is debatable whether that was truly the result, and in any case, on the street there really is little opportunity to find out.

So forget about it. Clean and service your carbs correctly and they will work famously, much better than many claim, and you'll never think about those modified holes.

There is a ton of this out there. But let's take just three items: stroking throttles, burnishing float valve seats, and using pliers on float pivot pins.

Stroking throttles: If you look closely at the throttle plate of a modern CV carburetor you'll notice the plate's edge is not machined at 90 degrees, it is rather at an oblique angle; it is in fact a knife edge. This angle accomodates the angle that the plate is itself mounted in the carburetor, so that the edge of the throttle plate seals perfectly against the carburetor body. And, the throttle plate is either brass or even softer aluminum. Dragging ANYTHING under the exquisitely-machined surface of the throttle plate is a crime. Whether wire, or a plastic tie, drill bit, whatever, the throttle plate is not going to survive this nonsense without damage. The resulting groove scratched into the edge of the throttle plate will pass more air than the plate's position willl call for, throwing off everything -- synchronization, idle speed, the works.

Burnishing float valve seats: A couple of how-to books on the 'net instruct to use an abrasive to "clean" float valve seats. I cringe every time this comes up in conversation or I see it mentioned on user forums. I have contacted one of the books' authors, who was responsive to suggestions, and that is good. I have two problems with burnishing float valve seats. One, it has the real potential of changing the shape of the carefully machined taper in the seat, and worse, even making it out-of-round. That's bad enough, as the seats in many carburetors are not replaceable and thus the carburetor body itself is ruined. Two, there is more than just potential but real danger, in another result of burnishing and that is changing the height of the seat's sealing surface relative to the carburetor casting. This is bad because many mid-80s Keihins have non-adjustable floats. So changes to the height of the float valve seat necessarily changes float height also, and it can't be compensated for. I recently had on my bench a very valuable Euro model CB1100R set that suffered from these two issues. How long is it going to be I wonder before folks stop doing this?

Using pliers on float pivot pins: Broken float pivot stantions are a fairly common finding on certain models of vintage carburetors, when the previous mechanic has not been careful. Though obviously heavy corrosion around the part can lead to failure, even when there is not significant corrosion, the stantions may still snap, if the pivot pin is not removed correctly. And correctly means with a properly fitting drift, not a pair of pliers. The use of pliers puts divits on the pin that make it seize in the stantions, resulting in breakage of the stantions during installation or more commonly, during a later removal.

There are folks rebuilding carburetors who shouldn't be. Who have no background in powersports. Who don't bring to the task an understanding of mechanics. These are the folks who using vapor honing as a cleaning method.

Vapor honing, or more accurately, wet abrasive blasting, is an increasingly accepted method of restoring the finish on all kinds of aluminum parts, including carburetors. I use it, and though it requires some very careful technique to avoid problems, it is a valid procedure.

But it is external only. It is a surface technique. However, as with engine parts and for the same reasons, when used on carburetors, the carburetors must also afterward be cleaned, and this is even more important after shooting abrasives into them.

The valve's sealing area is its angled face. This precious, precisely-made surface is reasonably tough, but over time it gets pretty beat up. Spring tension, combustion's forces, and the camshaft's relentless pounding -- all combine to wear this face, eventually producing on it a ridge or ring, the imprint of the cylinder head's valve seat. This classic valve wear is called recession, because the valve actually gradually withdraws into the cylinder head. Normally, recession happens very slowly. In our grandfathers' day 30,000 miles was common. And it was easily corrected. The valve was removed from the engine and its ridge ground out on a special machine that had a super-smooth grinding wheel. You might be familiar with this.

But 70s and 80s vintage Japanese bikes are unique. You don't grind their valves, and recession on them is a whole 'nother story. On May 4, 1971 Honda issued Service Letter #84 titled, "Intake and Exhaust Valve Refacing - Not Recommended". The bulletin heralded a sea change about to sweep the Japanese segment of the motorcycle industry. The backstory was that no longer would Japanese makers' valves be made the traditional way, of two pieces welded together, the valve's head of a material optimized for its role and the valve's stem similarly of a unique metal. From this point on, the valve would be a one-piece forging, and a new thing, a thin plasma coating called Stellite, would be added to the valve for durability. The bulletin's succinct message was that due to this coating, and in a departure from standard automotive practice, this new-age valve could not be refaced during an engine rebuild. Replacement was now the only option.

However, it soon became painfully obvious that these new valves were astonishingly soft. By 15,000 miles and in many cases (such as in early 80s Kawasakis) sooner, they were badly receded, i.e. their sealing faces ridged -- despite the Stellite -- and had consequently lost sealing ability. This prevailed for many years. In fact it wasn't until almost 1990 that Honda and the other Japanese manufacturers would catch up to the issue. Thus for a model range of almost 20 years, Big Four bikes suffer the curse of soft, fast-wearing, throw-away valves, and all of these engines exhibit abnormally (and often seriously) low cylinder compression as a result.

In fact, low compression is the first and most significant practical consequence of these cheaply-made valves. All vintage Japanese engines, unless the valves have been replaced recently, need a valve job. All of them. The symptom is significantly low compression, typically a loss of more than 35 percent. Instead of 170 psi they exhibit just 110 to 130. Proper tuning of these engines is very problematic until they are repaired.

An added consequence of unusually fast valve recession is the valve moves steadily upward toward its tappet, reducing precious clearance. This further reduces compression and more importantly, also reduces valve cooling, leading quickly to burnt valves. In many engines, recession happens so fast the rider is aware of it only when discovering serious engine damage.

A third problem is ignorance. Many mechanics persist in refacing these valves. That is, grinding the valve's sealing face as was common until the 1970s. But removing a Big Four manufacturer's valve's special coating can cause it to quickly be heat damaged and will certainly increase its already rapid recession rate. The correct way to handle receded valves is to replace them. Some folks default to lapping the valve, that is, rubbing the valve against its seat with an abrasive paste in-between. Though countenanced by some manufacturers, lapping is a hack procedure. It does not address recession, but instead makes recession worse. At most consider lapping a "get it home" effort and no more than that.

The purpose of valve clearance is to compensate for heat expansion, right? Wrong. This hoary, tenacious assumption may be intuitive, but it is very wrongly so. Actually, as the valve in an overhead cam engine heats up, it expands more than the castings around it, resulting in the head of the valve increasing in size and the valve consequently being pulled into the combustion chamber, increasing valve clearance.

Why then, clearance? Valve clearance is wholly a product of cam lobe design (shape). It's tied to the specifics of a cam's intricate geometric design. A cam lobe is not just an ellipse machined onto a shaft. It's a complex shape with several distinct radii, each with its own job to do, and one of those dimensions is where valve clearance comes from, as we'll see. Let's start with the "base circle", also called the heel. The base circle or heel is that part of the cam lobe that looks mostly perfectly round, a constant radius. It's the datum line, home base, the point of departure from which everything else on the cam is measured. It is also the valve's fully-closed point, giving the valve its cooling time. Opposite the cam's base circle is the "nose", the point at which the valve is fully open. The nose affects valve open spring pressure, an important consideration in engine tuning. Either side of the nose are relatively flat areas called "flanks". They open and close the valve. On some cams the opening and closing flanks are symmetrical. But not on all of them. In addition, shim type engines, rocker arm engines, and pushrod engines each have their own distinct flank shapes, most flattish but a few more rounded.

But the most interesting of the cam lobe's parts and one with many secrets is the "ramp". Detectable only with a dial indicator, the ramp is the tiny transition zone at which the radius of the base circle becomes the broad, almost flat surface of the flank. Though complex in design, the ramp's job is simple: to cushion the valve. For a handful of crankshaft degrees, the ramp eases the valve into its sudden climb up the lobe's opening flank. Then after the valve has opened and is skiing down the closing flank, it comes to an identical ramp on the closing side of the lobe that gently decelerates the valve so it doesn't crash onto its seat.

Paradoxically, there isn't actually room enough on the cam for as much transition as the valve really needs. Here's where valve clearance comes in. Valve clearance supplements the cam's built-in cushion, augmenting the always-minimal ramp. Different motorcycles have different valve clearance specifications because they have different cams with different amounts of ramp. Modern engines run three to five times the valve clearance of engines of 30 years ago because their cam's larger lobes cut into the ramps, making them smaller. Less ramp means less opening and closing transition-- big cams need more valve clearance. Small ramps go with big valve clearance, large ramps with small clearance. Heat has nothing to do with it. 2

And neither does noise. Valve clearance has nothing to do with noise control. 3 Many seem to believe that should an engine develop a slight ticking noise this means the valves are out of adjustment. Actually, there is little direct connection between the two. I have known customers who wouldn't adjust their valve clearances until hearing this ticking, as if the whole reason for adjusting the valves is to ensure a quiet engine, and conversely, who believed no noise means all is well, no need to adjust anything. If the former is ignorant, the last is dangerous. It is not for nothing that factory valve clearance adjustment intervals are spaced just 3,000 miles apart on 70s and older Hondas. It's a very important part of maintenance, second only to ignition service. In another post we'll expand on the kind of wear that makes valve adjustment necessary.

I knew a mechanic who obsessed over getting valve clearances exact, to the point of using a dial indicator in place of a feeler gauge. This is silliness. Valve clearances are not akin to carburetor jetting or piston-to-cylinder clearance, a specification indelible, sacrosanct, unchangable without marked consequence. Have you ever noticed that, much like spark plug gap, many engines' clearance specifications are given as ranges? Valve clearance is all about valve cushioning, remember, ramps, and has nothing to do with heat or noise or demandingly exact valve timing. 4 Knowledgeable mechanics have learned to be relaxed about clearances, opting in most cases for slight looseness, and nearly every old timer has long since discovered that increased clearances helps the engine in numerous ways. It forestalls the valve's eventual burning due to insufficient clearance. It increases the valve's ability to shed carbon. It adds valve cooling time. It lengthens the engine's compression phase, boosting cylinder compression and by the same token shortens valve-open time for increased intake air velocity that improves low rpm performance. These are real world benefits long understood and valued by career techs. Don't minimize them.

The official manual describes a camshaft measurement routine that is often misunderstood. It has you measure the entire cam lobe, heel (base circle) to nose. While having a purpose, the actual outcome of this measurement is not to gauge the potential of your cam or compare it to another cam. You can't do those things by this measurement; it's too gross, it spans too many of the cam lobe's important regions all at once, areas of the cam that need to be separated to get meaningful specifications. The goal of the manual's measurement is maintenance, not performance. It's not intended to tell you anything about the cam's specifications. It is simply a crude and easy way to track cam wear, and you'll discover an astonishing rate of wear doing this. Japanese standard model motorcycle cams wear very quickly.

Some feel that measuring heel to nose and then measuring again ninety degrees to that across the heel, then subtracting, is a way to derive the cam's valve lift specification. As with many things, this sounds good but ignores reality. Three problems make this idea unworkable. First, the cam's heel or base circle is not necessarily continuous for 180 degrees, in fact in most cams seldom is. Remember the ramps? So you're not really measuring the base circle with your micrometer at ninety to the nose. In fact you're not measuring anything of any consequence. Second, when the cam is from a rocker arm equipped engine, the cam's movement profile does not match the valve's; the engine sees different movement due to the rocker arm's ratio. Therefore valve movement, both duration and lift, on rocker arm engines is most accurately measured at the valve itself. Engine builders actually do so on all engines, whether equipped with rocker arms or not. It's that critical. Third, even on a given model engine, the cam's base circle diameter changes slightly from year to year, making the heel to nose measurement of absolutely no use in comparing cams. You can tell almost nothing significant from measuring the size of a cam lobe. The manual's reason for doing this is to track cam wear and nothing more.

It's actually a bit more work to properly measure a cam. The most important, most useful, and most widely used cam detailing method is what is called "profiling" the cam. The cam is left in the engine, a degree wheel is affixed to the crankshaft, and a dial indicator is placed onto the valve. As the crankshaft is rotated, the indicator's readings are marked on a piece of graph paper every five degrees, and the result is a right-angle, X and Y, duration and lift depiction of both the intake and exhaust valve movement caused by that cam. This is a tremendously useful tool for getting a meaningful "snapshot" of a cam, and thus for comparing camshafts. Because it requires the same tools and setup, engine builders add yet another layer to this process that measures valve-to-piston clearance at various crankshaft positions, for a very complete picture of cam action. After reading this you might think cam profiling a very esoteric exercise. It's not. No one who properly modifies an engine neglects this.

Now let's combine ramps and measuring. We've learned we have acceleration ramps which gather up the clearances in the valve train before the valve is shot off its seat, and deceleration ramps which decompress those bits and cushion the shock of the valve's closing. And that they are what determine valve clearance. The problem is that these ramps accelerate the valve so slowly that interpreting exactly when it has opened or closed is difficult. Because of this, engine builders have developed a method of ignoring the ramps when profiling a cam. The ramp isn't there to move the valve anyway, its sole purpose is to graduallly take up clearance. Builders disregard the valve's movement until it has moved a certain amount, then start recording it on the graph paper, thus ensuring that the valve is well clear of the ramp. That delayed amount is called the "checking height." A checking height is merely a predetermined starting and stopping point in cam measurement.

This is great. It firms up the process of measuring the cam, makes it more accurate. But the problem is that ramps aren't all the same size. The ramps on a pushrod engine's cam for example are huge, because that engine's spindly valve train demands very gentle opening and closing curves. The ramps on overhead cam engines by contrast are much smaller, because there are fewer valve-related parts flailing about needing cushioning. Each engine design has its own size ramp and correspondingly its own recommended checking height; some 0.020", others 0.040", and still others 0.050". Comparison of these different cams is impossible, as two different checking heights give two very different measurements. What's needed is a system of measuring cam timing which is independent of the checking height used. Is there such a thing? Yes! That's the lobe center method. That is why it was developed. Though it still requires the use of a checking height, the lobe center approach indexes the cam based on an *average* of its opening and closing points -- the cam's "center" -- and not one of those points, then counts the number of crankshaft degrees from there to top dead center (TDC). This means different checking heights can be used on two different cams and this will have no effect on the timing numbers because no matter what the starting and stopping points are, the center of a thing is always the center. Make sense? Lobe center divorces checking height, once an insurmountable hurdle in ecumenticizing cams, from cam measurement, making legitimate cam comparisons possible.

You might argue that no one compares the cam from a Harley Big Twin with that from a Hayabusa and of course you're right. That isn't the kind of comparison we're talking about. Then why do we need the lobe center method to compare two cams for the Hayabusa? Their checking heights will be same, won't they? That's just it, they won't necessarily! Cam makers, each one having their own history and influences, continue to use different checking heights even on cams made for the exact same model motorcycle! Why then isn't the cam lobe's center measured directly? Because it isn't the lobe's *physical* center we're looking for, it's its *mathematical* center -- the average of its opening and closing points. In some cams, the physical and mathematical centers are the same, but not in all cams. The cam lobes in overhead cam rocker arm engines for example are asymmetrical -- their opening and closing flanks are shaped differently to compensate for the change in geometry the system undergoes as the rocker arm slides over the lobe.

So that's lobe center. However, an odd thing has happened. In recent years lobe center has been appropriated by many for use in timing cams to the engine instead of merely comparing cams. They propose that a particular lobe center works best on a particular engine design, i.e. larger lobe centers on Kawasakis and smaller ones on Hondas. An intriguing idea yet I'm not sold on it. I think it's pretty arbitrary. In my view it obfuscates the real goal of adjusting intake valve timing and assumes a kind of wavelength-of-kryptonite-struck-with-a-hammer forensic precision that is unrealistic and unwarranted. In any event, there is nothing wrong with using lobe center for timing, if you want to go to that trouble, other than it unnecessarily adds to and ignores the most important valve timing event, intake valve opening and/or closing.

A four-stroke engine's cylinder firing order is largely determined by its camshaft. A couple of examples. Generations ago, Yamaha 650 twin racers used to run cams that were cut in half and welded back together to make the engine fire its cylinders in a different arrangement for improved traction, and presently owners of these vintage bikes in search of enhanced engine smoothness are doing something similar, that is, rearranging the cam's lobes. Also, the exotic six-cylinder Honda CBX1000 had an error in its earliest official manual that when followed made the left side cams 180 degrees out, resulting in such a dramatic alteration from the bike's 1-5-3-6-2-4 firing order that all of this engine's famous silkiness was eliminated and the cam chain failed within 25 miles from the stress.

The engine's phases depend on inertia -- the intake charge's momentum keeps it flowing into the cylinder despite the piston's upward movement after completing the intake stroke. Delaying the intake valve's closing to take advantage of this phenomenom increases cylinder filling and power. That's good. But it's kind of tricky. How long is long enough? If the valve is held open too long, the mixture's momentum dies and the gases back up in the port, sucking mixture out of the cylinder and causing a loss of power instead of a gain. On the other hand, if we close the valve too early, we've limited how full the cylinder can get. Either way, power is lost. The ideal thing is to close the intake valve at precisely the millisecond the mixture loses its momentum and stops, but before it reverses direction. This is the whole point of making sure the cam, and in turn the intake valve, is in the correct position to make this happen. Whether manufacturer or modifier, this is what you strive for.

However, the manufacturer plays to a more careful set of rules. The result is the stock cam times its valves conservatively, providing the cylinder very limited exposure to the atmosphere, unlike the performance camshaft's extended timing which exposes the cylinder longer. This is because etended timing harms air velocity and density. Therefore, though the engine's power can be increased through inertia tuning, that increase is focused more around a particular rpm range, and not spread as broadly over the rpm as before. In fact, the "cammier" the engine, the less power it might have even than stock at most engine speeds, making added power only at the one that coincides with the ideal inertia rpm. Moreover, that rpm will be higher than normal due to the resulting slowed intake air speed, which reduces combustion efficiency due to reduced fuel and air homogenation. Combustion, and thus torque, suffer. No free lunch, as they say.

This well-known drawback can be partly overcome by nudging cam timing to put the intake valve's closing at the point that captures that last little bit of the intake's inertia, just before it falls, closing the door on it, so it can't back up. As described earlier. Trial and error finds this ideal point that maximizes cylinder filling and pressure and is the whole reason behind "degreeing" camshafts. Degreeing a cam is not simply mistiming it. The nudge is less than one-third of one sprocket tooth's distance. More on this in the next post.

Cams remanufactured to stock specs, in which there is a growing popularity, often outperform bigger, "high performance" cams. Many times my customers have asked for bigger cams. I generally discourage them. When they insist they always find they have made a mistake. "I've lost my low end", one says. "Your engine is over-cammed," I reply. No one wants to believe it. They have to experience it for themselves. Something few seem to appreciate is how well the stock cam works in most Japanese multicylinder engines. Short of riding at full throttle, i.e. racing, aftermarket cams usually fail to satisfy. For the kind of riding most of us do, stock cams really are best.

Common wisdom on the Internet is that forged pistons are superior to cast ones. This is false. It's true that most aftermarket pistons are forged, but that is due more to manufacturing realities than to product superiority.

Three things cause forgings to characterize the aftermarket. First, very small production runs. The aftermarket piston market is a tiny fraction of the OEM market. The equipment OEMs use for casting is very costly. The aftermarket resorts to forgings for cost considerations above all else. Second, and not far behind, durability when abused. Most aftermarket users are assembling heavily-modified and stressed engines needing pistons that can suffer unusual abuse such as repeated detonation. This suits the forging well due to its more dense metal grain structure. And third and equally important, customization. Performance engine builders prefer the freedom forged pistons offer of excess material on the crown with which to customize the piston top to their needs, something that cannot be done with minimalist cast pistons. For these three reasons, forged pistons rule the non-OEM piston world.

However, forged pistons demand many compromises. First, the clearance that the forged pistom must be installed at is often considerably more than that of its cast counterpart, due to the less stable material the forged piston is made from. Second, the typical forged piston's aforementioned extra crown thickness that is such an advantage to the knowledgeable engine builder is on the other hand a liability to the home mechanic who has no intention of customizing the piston tops. The unwanted extra mass makes the piston heavier which results in more engine stress. And third, many forged piston manufacturers seem to struggle in manufacturing the piston's pin and its corresponding bore in the piston. For example, pins made of lessor grade material than stock and then chrome plated to compensate. Piston pin bores that are either too loose or too tight. And, pin retaining systems that differ considerably (and inexplicably) from the excellent stock method. These are all issues with forged pistons. Some aftermarket piston makers even dispense with retaining clips altogether and have you put plastic buttons on the ends of the pins (an obvious low-cost "out")! I have seen what those buttons look like after 10,000 miles. Not inspiring.

There are some excellent manufacturers of aftermarket pistons today, many more than there were 40 years ago. Wossner, JE, and several more. Even CP, a division of the high performance connecting rod maker Carrillo. But a forged piston is not categorically better than a cast piston. Better in certain applications. Better when modification is necessary. Better when it is all you can get. But not categorically better in all cases, and for many, actually inferior.

A motorcycle magazine editor once said he didn't see the problem with using silicone sealer. Two things seem obvious to me in this. One, it acknowledges there is pushback, and there certainly is. In my more than 46 years in this industry, I can't think of anything that says "hack" more than silicone sealer. All good mechanics feel this way. And two, this editor's statement only emphasizes the lack of credibility of mainstream powersports media, the same media that wants you to believe the knurl on a screwdriver blade is for gripping with pliers.

When I was in the service trenches in dealersips and independent shops, a good way to lose the respect of your shop companions was to let them see a tube of silicone sealer in your hand. We're talking major problem here. There are many kinds of sealers used around engines. BMW even had one (Dirko) that was nearly epoxy-like, and actually came with their car's replacement head gaskets. And then there's Rolls Royce specified Hylomar, at the other end of the spectrum in its never-hardening, forever tacky, chewing gum-like consistency. Different products for different uses, right? Naturally. That's decision number one: the right product.

For Honda crankcase halves, there is nothing better than Hondabond 4. Created by Threebond and similar to that company's products as well as many other offerings by the Big Four, this is the factory stuff: non-hardening, very tacky, good-sealing. The problem with silicone sealer is it has no body. This means it doesn't resist being squeezed into nothingness, and it means the product has no surface tension. Whatever blobs form, even the tiniest ones, are prone to breaking off and falling into the engine's oil supply.

Here is an error that is repeated mindlessly all over the Internet. The cam holder bolt torque specs in many OEM manuals are incorrect, and Kawasaki and Honda at least have admitted it. Using these specs results in over-torquing leading to bolt failure, and worse, distortion of the cam holder, which has resulted in cam seizure. The factories often specify 12 or more foot-pounds for these 6mm holder bolts, nearly double the proper specification and close to that for a spark plug!

A foot-pound torque wrench is never the right tool for a 6mm bolt. Deadly. A first-semester tech school student knows better. What was Honda thinking? As with many gauging tools and devices, when used at the extreme ends of their scales they are the least accurate, and you certainly want accuracy when tightening. Not to mention the all-too-handy extra length of a foot-pound wrench that naturally promotes heavy-handedness. Properly short wrench and inch-pounds only on bolts that small, thank you very much. In fact, a 6mm bolt threaded into aluminum is never tightened to anything over 90 inch-pounds (equal to 7.5 foot pounds, a bit over half the figure in common use). A lot of damage has been done in this area, especially regarding cam holders.

And yet another peculiar Internet ethic. The most active vintage Honda four forums regularly promote removing the alternator cover and using its bolt to rotate the crankshaft during maintenance such as valve adjustment requiring the crankshaft to be rotated. Pretty peculiar, this.

I suppose the reason is someone on some forum somewhere had an issue with the part of the engine actually designed to be used for that, the ignition advancer and its hardware. But I have never had a problem and I know of no other career machanic who has. Just as with virtually everything else forums turn upside-down, why don't they instead encourage repair of the offending part? Makes sense to me.

It is extremely common for folks on the Internet to excuse the poor cylinder compression of their newly-assembled engine with the excuse, "Oh, it still hasn't broken in yet." This is silly. The fact is, due to the high precision of manufacture and assembly required by Japanese top end parts, they dot break in. The cylinder compression of a properly rebuilt engine will be the highest it will ever be minutes after startup, before it even leaves the shop. It will not increase with miles.

Why then do Japanese powersports manufacturers specify break-in periods? Two reasons. One, the less precision manufactured bottom end components such as the transmission will slough off some forging and casting flash, wear in a few rough spots, and of course the first oil change will purge out the resulting contaminants from this process. But that's pretty minor and largely theoretical. More importantly, the manufacturer specifies break-in as a chance to catch faults in manufacture: circlips not fully seated, fasteners lacking proper torque, misassembled directionally-oriented parts, misaligned gaskets, seals or o-rings ruptured during installation, and to confirm the quality of such vendor-sourced parts as bearings, seals, chains, belts, springs, etc. Thus break-in as a concept is more a warranty thing than it is a mechanical requirement. Never let someone tell you your newly-assembled engine needs to break in before it will have the correct cylinder compression. It ain't so. That engine was improperly assembled.

A lot has been said on the Internet about the failure mode of first-gen Honda V4 cam failures. And it's all wrong. Lubrication has nothing to do with it.

At one time there may have been as many as a dozen different oil hose kits available. These kits exist solely due to a misunderstanding. The orginator of these kits probably observed that Honda's race team was using handmade external oil lines on its Interceptor-based racebikes. The assumption was apparently then made that this was to counter cam wear. Before long, everyone "knew" why V4 cams failed. However, there really is no connection, not on the race bikes and not on consumers' bikes. The race bikes used braided oil lines simply because the stock soldered steel oil lines cracked when the machines were used hard, something that is well known.

Ask a mechanic about lubrication-caused cam wear. Career mechanics are not confused about this early V4 cam failure. They know it has nothing to do with lubrication, because they know what lubrication-starved cams look like, as does the motor industry in general. What you see when the cam has worn excessively due to poor lubrication is damage that looks like the cam was turned on a lathe. A dramatic, obvious, cutting appearance, with surrounding areas deeply discolored -- blacked -- due to heat. This is not what happens on the Honda V4. Those cams get a more crumbled cheese look.

What then causes V4 cam failure? It's simply the failure of the engine's chromed cam followers (rocker arms). This is something that happens to virtually all follower-equipped Honda engines. The chrome eventually gives up, begins to peel, and the follower then becomes a cheese grater and tears up the cams.

The V4 engine is however unique and experiences this syndrome much earlier than do other Honda models. The reasons, four of them, have to do first with something that every manufacturer does, and that is they make cams very economically by casting them almost to size then lightly grinding them to final dimension. This technique produces cams that tend to have pockets of impurities just below the finished surface. Once the cam has worn a bit, and Japanese cams wear fast -- about 0.001 inch per thousand miles in the worst cases -- these pockets, if present, can be uncovered, break through if you will, and this results in that crumbled cheese appearance of the cam lobe that is classicly famous on the V4.

This pockmarked cam lobe then, combined with the V4 models' high valve lift and the extreme pressure exerted by dual-spring-equipped tandem followers, is what hurts the chromed follower more aggressively than on other models. Once the follower starts peeling, it's all over. The follower attacks the cam, grinding it up. And every engine that has this combination has suffered the same cam failure fate, with Kawasaki's ZX900 series are a prime example.

You can see too that this explains why some V4s have the cam problem and why some don't. Pockets vary in occurance and in size. Some cams don't exhibit them at all, and some have pockets that when they apoear are so small there is reduced or no consequence to the follower.

Porting. There are two completely different worlds when it comes to cylinder head porting. It's not at all what most folks think.

One of those worlds is the lowest common denominator one characterized and promoted by Internet user forums. It's a hatchet ethic. You know, cut and slash. The same ethos that has folks cutting their frames and throwing away their airboxes and sawing off their mufflers. The adolescent carving on the schoolbench with a pocket knife. Cut, cut, cut. Kick it down, bust it out, tear it up. Carve it, kill it, blow it out. Kind of a cylinder head enema. Very few understand that the porting practiced by professionals is actually very scientific, and this is the second world, the real one. Where flow and area and angles and velocity and more, are the bywords, the metrics. Not a haze of aluminum dust.

No matter what reputation a person has attained, if their porting work is not accompanied by before and after flowbench graphs, it's voodoo. Don't trust it. There are thousands of ways to do porting wrong. And very very few ways to get it right. And along the path between the two are some awesome, coming-of-age, almost life-changing experiences. The flowbench and accompanying velocity probe are the judge and jury, and submitting yourself to them is very sobering. Very humbling. You disciver very quickly it's not what your eye sees that's important. It's what the air sees.

I taught porting and flowbench use at MMI, so I have in mind three tips. One, the would-be porting pro must ruthlessly expunge from his mind the idea that porting means wholesale metal removal. Porting sometimes means putting material into the port. Yes, into. Two, the wielder of the porting tool must zealously preserve port cross-section as a dogma, a religion. Changes to the port must not result on a larger port. The point of porting is to put the port and its air on friendlier terms, and this is antithesis, counter, to making the port larger. You may not believe this now, but you will. Porting is really all about angles. Optimizing them, increasing radii, thinking like air would think. What does it want? Where is it going? What will be its behavior at this point in the passage? Is it slowing or picking up speed? Can it be cajoled, tricked, coaxed? And finally, three, the most important work you can ever do in a port takes place within an inch of either side of the valve seat. Meditate on that if you understand engines.

The Internet, in its inimitable style, promotes a lot of things professional mechanics would find objectionable. That is, if they actually visited forums. Hundreds of things, actually. One thing almost every forum's engine repair thread includes is the mention of honing in-service cylinders.

Likely the notion of honing in-service cylinders originated when engines were basically solid cast iron and had low-tech pistons, the combination requiring clearances of several thousandths of an inch. During this same era, piston rings weren't the best either and benefitted from fairly aggressive cylinder finishes to facilitate break-in. However, the Japanese have always done things differently. Take a look at the clearance specs in a Honda manual, and then note the brand's tin-coated top piston ring. It's a different world entirely. Very few Hondas are assembled with more than 0.001" clearance and most at quite a bit less than that.

The problem is, using a hone in any in-service senario is going to destroy this delicate fit. I know, many of these folks are merely trying to derust their cylinders and put the bikes back on the road. I get that. But it's still bad practice. When rust is the issue the right tactic is to bore the cylinders. But the real tragedy is all those motorcycle forum visitors who are being encouraged by forum "experts" to hone every time the cylinder is removed, or when fitting new rings. This is patently bad practice. The cylinder does not need to be honed simply because it was removed, or because new rings are fitted, and doing so will ruin it by increasing the bore size and upsetting the precise piston fit. The only legitimate use of a cylinder hone is as the final step of cylinder boring. Back up and read that sentence again. Any other use is hack. That is, ill-advised bad practice, i.e. misuse. Plain and simple. Because it makes the cylinder artificially worn out. It doesn't take a PhD to see this once you understand the close tolerances of these engines. And so many forum members wonder why their engines smoke, use oil, and run poorly.

Some have pushed back that the official manual allows a broad leeway in piston-to-cylinder clearance. Not so. This is a misread of the manual. Honda manuals communicate two specs. One is the assembly spec, what General Motors in their manuals calls Production Fit. The other is the service limit, often multiple times assembly spec. When that engine is apart for rebuild, you are working to the assembly spec, not the service limit. The service limit is worst-case scenario, i.e. you are a missionary in Uganda and the nearest competent machine shop is an ocean away. I mean, why bother with an engine rebuild if you're going to reassemble it worn out? Argue this all you want, it won't change the reality.

Something career mechanics have known seemingly for eons is that loose valve clearances are better than tight ones. Forum people don't like this concept of loosening the valves. They are offended and intimidated by something outside the scope of their experience. One of the truly regretful situations is what these forums have done to pervert the knowledge base that was at one time accessible and helpful to everyone.

There are many benefits. For example, unless a valve job has recently been performed-- and sadly many times even if it has-- loosened valve clearances can recover significant amounts of engine compression lost due to valve wear. And wear of this kind is endemic to vintage Hondas. Loosening valve clearances, though no substitute for the needed valve job, often restores a measure of compression and results in performance improvement. Second, even on an otherwise healthy engine, loosened valve clearances boosts midrange. This happens through the very fortuitous outcome of shortened intake timing while at the same time no change to actual cam timing or to valve lift. A third benefit involves carburetion. Many of the carburetor tweaks-- for example jetting kits that richen-- made to vintage Hondas are effective because they compensate for low compression caused by leaking valves. Once compression loss is at least partly mitigated, those tweaks become ineffective, unnecessary and even harmful.

Don't let anyone tell you that just because the manual specifies a certain valve clearance that this figure is sacrosanct, inviolate. Nothing of the kind. And career mechanics know this very well.

Probably the area most in which the most bad advice is given on forums is in electrical. Charging and ignition systems in particular.

Forums consistently promote Dyna and other points replacement ignition systems, touting them as both maintenance eliminating and performance enhancing. At best, this is very misleading. While it can be argued Dyna ignitions and their kind do eliminate the need for regular adjustment, beyond that the promise of reduction in maintenance effort is a phantom. First, a Dyna ignition requires just as much work to install as the stock points system, due to defects in the product that demand very creative modification so that the stock advance curve is maintained. In addition, Dyna's individual modules usually themselves require timing, also adding to the work of installation. Thirdly, while further adjustment once properly installed is unnecessary, properly set up points systems also last as long as 10,000 miles with little to no adjustment, thereby making an electronic ignition's benefit in regard to maintenance of much less value; in fact, basically nil.

The points replacement systems that simply add transistors to the points to reduce the current the contact points must carry, retaining the points and presumably lengthening their life, is a very noble and clever idea. But more than anything it's an answer to a question no one has ever asked. Please take note: There is no high-current fault in Honda point ignition, no wear, performance or durability deficit due to current. Any claim to this effect is a fallacy. Mechanics familiar with Honda points systems have been increasing their current load (through the use of aftermarket coils) ever since their emergence and have never experienced consequences, either in points life or electrical loading/battery charging terms. Due to their very high quality, it's hard to hurt OEM Honda points, and while exhibiting a quite humble output by today's standards, Honda SOHC four charging systems are more than adequate and able, even strong, on properly-maintained bikes. Arguments to the contrary are ill-informed, specious, and unnecessarily disallusioning to the unwary.

Charging system parts that are original factory, in good health, correctly adjusted (where possible), joined by dutifully-maintained connectors, and used reasonably-- that is, in keeping with their design context-- work just as well in 2021 as they did in 1969. They function quite well, quite adequately. It seems a popular pastime for forums to proclaim the contrary, warning that any change from the factory electrical specification will reduce the system's ability to charge the battery. This is so egregious a position as to merit the harshest possible sanction. Whatever their motivation-- and it boggles even speculating-- the forum "experts" who are proponents of this argument are doing the vintage Honda community a serious disservice.

As is typical on forums, there is silence regarding proper maintenance of these systems, while there is far too much noise depicting them as inadequate. If that does not give one a clue as to both the credibility and the apparent motive of these forum "experts" I don't know what does.