Exhaust discoloration
Customers frequently point to their discolored exhaust primary (“header”) pipes and mumble something about ignition timing or carburetor problems. While it is possible those things can result in discoloration, the original equipment exhausts on most vintage Honda streetbikes are double-wall--it’s pretty hard to heat-damage the chrome on them, and fuel and ignition systems would have to be really disfunctional for it to happen. But there is one sure way, and it is the most common one, and that is by an uncontrolled idle rpm. Whether during engine warmup or at any other time, if the idle rpm is allowed to creep over 2500 you can expect the exhaust primary pipes to overheat and discolor. This is in fact documented--warned against--in many official Honda owner’s manuals.

Carburetor fuel level
Many believe that the specified float level on a Honda carburetor is what it is for the purpose of liquid tightness. They therefore proceed to alter that level when experiencing float bowl overflow in hopes of stopping it. There are literally dozens of possible causes of fuel leaking from the carburetor, enough to put them into two large and different categories even. But fuel (or float) level is way down on the list, for one important reason: high fuel levels result in richness throughout the carburetor’s entire operating range. If float level was to blame for your carburetor overflow, long before complaining of that you would have got off the bike in disgust due to its running so badly. Think about it. Don’t try to solve carburetor overflow by changing the float level. Fix the actual problem, which the most likely on old Honda carbs--after bad float valves--is cracked overflow standpipes.

The clear tube method
The clear tube method of determining fuel level often promoted on the Internet for use on vintage Hondas is one of a myriad of things online communities take out of context. Early examples of non-Honda (Mikuni) carburetors had inherently very leaky float valves, thus the OEMs that used Mikunis--Kawasaki for example—had to use a fuel level measuring method that accommodated their carbs’ “dynamic” fuel level (as opposed to its static level). Yamaha also had this problem. Look around for Yamaha triples or XS1100 fours. Not many to be found, are there? So bad were their float valves that their roller bearing crankshafts wore out ages ago, due to fuel dilution of their crankcase oil. Though advocated on many Honda forums, the clear hose method is irrelevant to Hondas. This is proven by the fact that the procedure has no reference point in connection with Hondas, no standard. That’s because Honda never published and never adopted this method. They didn't need to. Honda uses the simple float height method because their float valves don’t leak. Do your Honda float measurement the Honda way, using the Honda tool, and the Honda method (with the carbs right-side-up, as Honda's 1960s and early 1970s publications show). You can't go wrong. The clear hose method is not one that is universal, is not a technique for solving float bowl overflow, and is not superior to Honda’s float height method. The forums are wrong in characterizng it as a superior way to do the job. It isn't.

Jet kits
There is an astonishing absense of discernment--what we used to call good judgment--in the powersports industy. Call it the YouTube syndrome. People gravitate to “silver bullets” that are at best placebos and sometimes a lot worse. Carburetor rebuild kits, “leakproof” fork seals, high-voltage ignition coils, baby oil packaged in a quaint “Mystery” container, Chinese piston rings, “lifetime” air filters, headlight relays--the list is long and infamous. Carburetor jet kits are in this same category. Everyone seems to think the Honda factory purposely jetted their carburetors too lean. Not only didn’t they, they couldn’t. The idle circuit is the most tenuous, the most sensitive, of all circuits to the point that it requires an adjustment screw to compensate for even slightly varying atmospheric conditions. Similarly, the main jet is carefully tailored to different export destinations, as well as richened up slightly for a margin of ensured rideability. Honda has always put in rich main jets. Anyone who has spent any considerable time around Hondas knows this, as does anyone who has experience tuning bikes on a dyno. As I have mentioned before, production road racers used to have us dyno-tune their production class machines for the racing season and this consisted largely of reducing the main jet size. This made the most power. But then when the racing season was over and autumn’s leaves were falling, the bikes were too lean to be streetable--they wouldn’t get out of their own way!--and had to be jetted back up. That richness margin is real. It makes the consumer product used in widely varying conditions viable. Factory carburetor jetting is not so lean it needs richening. Just the opposite. Yet, carburetor-fattening jet kits often do make engines run better in certain cases. How is that possible? Invariably, those kits are designed to work when valve adjustment, engine condition, carburetor cleanliness and adjustment, and ignition condition and maintenance are not what they should be, they're neglected, affecting engine performance. This is true to some degree in any example of a self-maintained vintage Honda. Such shortcomings often can be covered up by throwing more fuel at the problem. The purveyors of jet kits offer you a solution to a poorly-maintained motorcycle--a fix in a box. Because poor maintenance effectively leans carburetion by making demands on the carburetor that are beyond its design. Thus the jet kit, by adding fuel, covers up for this lack of maintenance. But it’s a Band-Aid fix. It’s a work-around, and not a very good one. More legitimately, jetting kits also can in many cases compensate for engine modifications, that is, changes to the intake and exhaust system. But for vintage Hondas at least, they do so very poorly. Such needed jetting changes are virtually always better implemented using parts available from Honda.

Part 13