Some interesting facts, advice, opinions and observations about the iconic and special GL1000. In no particular order.
Many online voices supposedly experts on the GL1000 are not. None of them have experience in a retail repair and maintenance environment.
The GL1000 is a unique machine whose tuning requirements are unlike any other Gold Wing and very different from most other motorcycles.
The GL1000's carburetors are derived from--though still slightly different than--those found on the earliest Honda automobiles. Many of the carburetor's parts interchange.
Official confirmation as well as the vehicle's parts prove that this engine was developed by Honda's auto division.
The GL1000's ignition system presents the greatest hurdle in tuning this engine. The necessary steps in timing the ignition are completely out of the box and familiarity with any other motorcycle is not an advantage. If you don't know these steps you will not get this engine running properly.
The idle jet rules the GL1000 carburetor. No other GL1000 carburetor circuit makes as much difference performance-wise as the idle jet. But it can be a challenge. It is the smallest jet in the carburetor. It is buried the deepest and often difficult to remove. The jet's hole is only 0.013" in diameter, meaning this: unless you just removed and cleaned it, count on it being at least partly blocked at any given time. Guaranteed. And lastly, the idle jet affects not only idle but also starting, accelerating from a stop, and even cruising--yes, cruising, at low load and low rpm. Nothing is more critical to a pleasant-performing GL1000. Make sure the jet is clean, and this does not mean merely blowing air through it. Also make sure the idle circuit's air bleeds (under the vacuum piston) are the correct sizes.
Forums talk a lot about carburetor slide movement in relation to engine performance. However, they miss three important facts. One, the GL1000's slide does not start lifting until after one-quarter throttle. Two, slide movement in this constant velocity carburetor lags behind throttle position. And three, the ratio of throttle to slide movement is not constant but changes with engine load.
The GL1000's carburetors are too large for the engine, especially the 1975 through 1977 model carbs. The 1978 and 1979 carbs were shrunken, and every four-cylinder Wing after the GL1000 was given ever smaller carburetors.
Though lacking an accelerator pump, the GL1000 carb set could have used one due its being oversized. But installing the accelerator pump equipped GL1100 carburetors is not the answer. Proper tuning that overcomes the GL1000's lack of an accelerator pump is the correct approach.
All of these bikes exhibit low cylinder compression. This is due to valve and cylinder wear. The first is easily remedied, the second not as easily because the cylinders are part of the crankcase and thus more work and demanding of much more skill to machine. Very few people bore this engine.
Just as with any 50-year old motorcycle, the GL1000 should not be regarded as a viable touring bike. This may hurt some feelings, but there it is. I am nuts about 70s Hondas. But I would never ride a 50-year old motorcycle very far--certainly not out of town nevermind out of the state. There isn't a single replaceable part on that bike that can be purchased from a brick and mortar store. Not even the spark plugs. Maybe a turnsignal bulb. A fuse. Maybe. Virtually every part you will ever put into that machine will be hard won--diligently sought out over long periods online, purchased with big dollars, anxiously waited on during delivery because either the seller was patently unreliable or he was in Bangkok, and installed with something approaching misgiving if it is not installed by someone like myself who has the experience to know what he's actually doing. These are the facts of life with a bike of this vintage. It's a great bike. But it is also demanding on the order of an obsession.
The number one thing is ignition timing. Don't think you know how. If you haven't done it, you don't know how. And even if you have, you still don't. You need to find out how, and it really needs to be done. But it is a difficult job. I know of no other seemingly simple maintenance task that requires as much skill as this one, and I've been at this for more than fifty years now. And unfortunately, the need for this adjustment is not reduced by an aftermarket ignition system. Worse, the proper procedure is not explained in the official manual. And it's many times more important than carburetor work.
Close behind ignition timing in importance is the use of the very best ignition parts. This starts with factory Honda Hitachi (or TEC) brand points. Be sure to get the first-generation Honda parts, preferably not the current crop of inferior Honda points and definitely avoid the Chinese stuff such as Daiichi.
The carburetors aren't difficult to service, but they are quirky enough that familiarity with other carbs won't help much, and mere intuition is likely to simply get you into trouble. These are 1960s-era Honda car carburetors that were converted by the factory for use in the debut Wing in 1975 and are unlike any other Honda carburetor, though they superficially resemble 70s CB450 units.
Nearly every GL1000 I see in my shop has poorly-maintained spark plug caps. They are usually very loose on their wires, and inevitably have aged into the 10K ohm range and require replacement.
If you have Dyna ignition coils on your bike, you should have been told three things. One, the stock GL1000 ignition coils are just as powerful as Dyna coils (back in the day Honda mechanics fitted them to SOHC fours as an upgrade). So you won't gain any performance from them. Fact. And two, Dyna coils come default with automotive type resistive plug wire. You can order from Dynatek non-resistive wire and that is what you should do. Three, Dyna coils may be the best replacement option simply on the basis of aftermarket quality. But choose the gray (2.2 ohm) ones not the green (3 ohm) ones and gap your plugs at 0.032".
Cylinder compression is vital in this machine. If it's below 150 psi using a quality (not a $49) tester, forget about engine tuning until that is corrected. And note: Worn cylinders and valves are the issue and finding someone to machine this engine's cylinders is a challenge, as is also finding quality rings and valves, though head work is pretty simple on this engine.
The idle jet is critical. It must be removed from each carburetor and "sized", that is, its size confirmed with a wire of known dimension. Sixty percent of this engine's operational finesse depends on this jet. And it is frequently neglected, and unless very recently looked at, almost surely at least partly plugged. Don't overlook this.
The rear wheel flange demands a goodly application of high-content moly grease. Honda still sells this grease. It comes in a squeeze tube and is also used as engine assembly lube.
Unplug your crankcase breather from the airbox. This will slow the inevitable sludge and carbon formation on the carburetor slides.
Do not use premium gasoline in your GL1000. This engine is already prone to accumulate carbon. Using anything that will accelerate carbon buildup is a bad idea, and this includes that snake oil of snake oils, Marvel Mystery Oil.
Shun carb rebuild kits. No professional carb rebuilder uses them, and no one who cares about their carburetors should either. Kits containing replacement jet needles and needle jets result in the most seriously negative alteration you can make to these carburetors.
One of the bad things about carb rebuild kits for the GL1000, other than the near criminal replacement of factory metering parts with Chinese substitutes, is the unfortunate fact that the o-rings for the primary and secondary main jets in these kits are incorrectly sized and tear when installing the jets. No o-ring supplier and no kit contains the correct o-rings. They are available from only one source, and that source does not sell to the public. Fortunately, finding a business that has an account with this source and will sell the o-rings retail is not difficult. One such retail outlet is Amazon, believe it or not.
The throttle shaft felt seals on the GL1000 carburetor are not vacuum seals, they are dust seals. As such they cannot be expected to solve an engine performance issue. If you're experiencing such an issue, diagnose and go after the real problem.
Twisted throttle shafts are virtually endemic to GL1000 carburetors. It happens when the machine is resurrected from the dead and someone inadvisably exerts extreme force on the throttle grip to overcome the varnish buildup inside the carbs. The delicate shafts easily distort.
Unless rebuilding your carburetors each season is your idea of a good time, use Sta-Bil fuel preservative. And since the time it takes for fuel to start to gel is less than the period between rides for most of us, use it full-time.
The GL1000 carburetor is very much at risk for corrosion. This is because it is made of zinc, not aluminum. Actually, it's an aluminum alloy but one that is unusually high in zinc, making the casting extremely susceptible to corrosion. The result is that these carbs can corrode badly. And it has little to do with ethanol.
An inexplicable design flaw on these carbs is that they have no overflow telltale system. In fact, no Wing carbs do, four-cylinder or six-cylinder. (Many of Honda's late model carbs-- V4s, CBRs, even cruisers, don't either.) This means that when the carburetors overflow-- and they inevitably will-- there is no outward sign, no indication. This is not helpful for maintenance and poses a potential deterioration problem for the engine as the engine oil is continually at risk of fuel pollution at any given moment.
Eventually every GL1000 will start to overcharge its battery. The design of the charging system (permanent magnet, three-phase) coupled with the historically inevitable failure of the voltage regulator, makes this a sure thing. Constantly feeding 16V @ 9.5A into the battery theoretically can make it explode. It can damage the lights also. The only reason that may not happen on your bike is the fact that the GL1000 is a voltage sponge-- its electrical system, and particularly the huge 18 A/H battery, sucks up all the electrical energy it can. But don't count on it. I see this overcharge often, and it is not a safe situation.
Stay away from K&N and Uni air filters. Neither filter well--especially the K&N, and the oil in the foam type tends to creep downward into the carburetors.
Easily two-thirds of the advice on popular GL1000 websites is not good information. Most of them don't even know the purpose of the hoses between the sides of each carb and the air chamber (plenum) and have been debating the necessity of static ignition timing for decades, despite Honda's documented preference and the experience of pro mechanics. And forum-based electrical troubleshooting advice is not real-world. There has unfortunately been a long history of misinformation about this model online.
All years of the GL1000 exhibit an off-idle hesitation. Even the better-tuned 78-79 models. There are different approaches to eliminating this performance glitch, and they are all easy and effective. But bear in mind one thing: the GL1000 engine will never throttle like a GSX-R Suzuki. This is a car engine, remember, with a massive inertia-storing automotive style flywheel that prevents instant throttle response. But careful tuning can make a significant difference.
Although considered a matter of preference and vigorously and incoherently debated on the 'net, the GL1000 like most 50-year old Hondas is ridden so little that it is an excellent subject for switching over from glycol brake fluid to silicone to prevent brake cylinder corrosion.
Like most 70s Hondas, the GL1000 starting system's archaically-designed, three-roller freewheeling (sprag) clutch is negatively affected by heavier oil and by synthetic oil. Also, long periods of sitting promotes moisture accumulation which results in rust in this part, further deteriorating its function. Watch out for this. The engine has to be removed to repair/replace this part.
The infamous alternator stator connector meltdown has got a lot of press on forums, but in reality it is only one of three electrical connectors on the bike that are prone to failing. The good news is the parts to repair them are readily available and the proper repair technique, while ignored by forums, simple and permanent. Stator failure is not linked to connector failure, despite assumptions, but it happens too. The engine must be removed to replace the stator.
Rusty fuel tanks are a hurdle on this machine. There are many approaches to repair but removing the tank and removing the rust followed by zinc plating is probably best practice.
Bonus tip! Proper GL1000 clutch adjustment is typically neglected, what with the restricted access to the pressure plate. Correct clutch adjustment on most Hondas involves a special procedure wherein the cable is completely slackened, then the pressure plate adjusted, then the cable slack removed and a tiny bit of slack left at the operating lever.
Honda part numbers incorporate a center section that identifies the model that the part originated on. Most of the parts on a new model were identified in this section as new to that model, of course, but several more common parts would also be identified as originating on previous models, typically oil seals, bolts and other fasteners, a few electrical items, etc. At the time of the GL1000's introduction in 1975, "371" was designated as the GL1000 model code, and many of the bike's part numbers naturally contained this number. Interestingly however, because the auto team drove the project and in fact designed the engine, some of the GL1000's parts have part numbers containing "600" codes instead of "371". This is because Honda at that time reserved numbers 600 and over for their cars and the GL1000 engine contains several Honda car parts.
Due to the very loose (well over 0.005") fit of the camshafts in their bearings, valve clearance changes dramatically as the camshaft rotates. Perfectly set at TDCC, at 90 degrees (180 on the crankshaft), the clearance will be close to double. Similar to most of Honda's 1970s engines, this is of no consequence, not even excessive noise. And it does not mean the cam lobes are mismanufactured. It's all in the loose fit of the bearings.
The GL1000 through GL1200 have massive crankshaft flywheels, standard automotive practice and just one of many artifacts of the bike's original automotive heritage. Because of this, you cannot expect the engine, no matter how well tuned, to have anything like the throttle response of say a GSX-R 750.
Another thing revealing the GL1000's automotive DNA is its "floating" piston pin. Something of a misnomer, this means the piston pin does not rotate in the connecting rod, but only in the piston. In every other Honda motorcycle engine and virtually all other powersports engines the piston pin rotates in both the connecting rod and the piston. A special auto-derived tool is required to remove the pistons because of this.
A third car attribute of the GL1000 is its carburetors, which were closely copied from those on a very early Honda car. The carburetor castings are nearly identical and many of the parts will interchange.
The GL1000 ignition system is the most unique and non-intuitive feature of this bike. Far from being as simple as it looks, it takes countless revolutions of the crankshaft and kind of heroic effort to set it even close to correct. It's an extremely fiddly system that extremely few have been able to master. See what I have said elsewhere on this subject.
Speaking of ignition, the GL1000 ignition coils run on two different voltages. On starting, the coils get full power. Then after, they run on reduced voltage. Seemingly another automotive anachronism, no one is really sure why this was done to the GL1000 and defeating this goofy setup actually yields improved ignition performance, with no durability drawback.
The GL1000 has ignition points that look like those in the 70s 450 twin. But don't be fooled. They are not the same and using 450 points results in reduced adjustability and despite what many say, no performance advantage.
Once spied in the text of a European Honda advertisement, it is likely the "GL" model designation came from the words, "Grande Lux", a phrase meaning the pinnacle and which we in the anglo world have irreconcilably and improperly bastardized to, "Grand Deluxe".
The GL1000 lacks an accelerator pump on its carbset. And it can use one. There are even folks who have managed to fit enough Honda car carburetor parts to give it one. And some fit GL1100 carbs which have an accelerator pump. But there is a much better and easier way to get excellent throttle response in a GL1000. This involves several tuning steps, the most effective of which is adjusting the pilot screws to 3 full turns out from gently seated. This makes the idle a little richer than it should be when checked on an exhaust gas analyzer, but it is worth it for the significantly improved throttle response it and the few other special adjustments (such as the 0.006" valve clearance) deliver.
Adjusting the valve clearance on this engine to 0.006" instead of the factory recommended 0.004" will increase cylinder compression by a minumum of 10 psi, with no drawbacks and an expected improvement in starting and low-speed performance.
As with any 50 year old Honda, the GL1000's engine will usually be found to be under-powered due to age and wear. Most of this is due to cylinder wear, though valve and valve seat wear will also be evident. Remachining the cylinders is a bigger job than on other vintage Hondas due to the automotive-like unitized cylinder and crankcase, so very seldom is this needful procedure undertaken.
The four-cylinder Wings boast four different carburetor sizes. The GL1000 has two different sizes (75-77 versus the smaller 78-79), the GL1100 its own smaller size, and the GL1200 carbs are smaller yet. This is because Honda gradually accepted the fact that the Wing was not a sportbike, despite being promoted as one in the earliest advertising. So little by little the size of the carb bore was reduced to move the powerband lower in the rpm range and make the bikes more suitable for heavy road use.
There is a significant party of GL1000 single-carb conversion advocates. The truth is that few if any carb conversions go exactly as planned. Carb manufacturers do not make their products easily adapatable to other engines in the sense of tuning parts avaiability and you should know that it can take years to get to anything approaching adequate performance and not many have been satisfied with the outcome. Moreover, the original carburetors once prepared properly work outstanding and proponents of conversions are folks who have been frustrated--due to poor work and/or parts--with their stock carburetors. However, the factory carbs are not difficult to service, they just require a bit more than a "dunk and rinse" rebuild ethic.
Although for almost twenty years centering around the early 1970s Honda put valves in their powersports engines that were made cheaply and so soft that they receded rapidly, resulting in such a steady loss of cylinder compression that by 15,000 miles 70s Hondas are decidedly below par, the GL1000 was an exception. The GL1000 escaped some of this trouble kind of by accident. Though it has the same soft valves as the other Honda engines of its era, its auto engineers, in specifying unusually (for Honda) soft valve seats, unknowingly gave the GL1000 and GL1100 something of a reprieve from the severe valve recession malady that plagued other models.
Along with many other vintage Honda models, the GL1000 has the reputation of melting its alternator electrical connector. Though alternator failure is sometimes experienced also, there is no correlation between these two things. Connector failure is due to the very old style open-back electrical connectors which to not seal off dirt and moisture from entering the wiring, and the fact that the wiring is crimped. Once these two things are addressed, the exposed connector by filling with grease and the crimps by soldering, the failures will stop. And, although several aftermarket sources have arisen in recent years, the connectors are available from Honda and always have been.
The GL1000 starter clutch, the part that connects and disconnects the drive function between the electric starter motor and the engine, has an above-average failure rate. Though not difficult to repair, the engine does have to be removed from the frame and the parts are long discontinued from Honda. Good used parts must be found, which will be a challenge.
The GL1000's reserve lighting unit is a black box that automatically turned on the other beam when one of the headlight's beams failed. The box itself was prone to failure and Honda actually recommended to its dealers that it be bypassed electrically.
The neutral light switch in the GL1000 has a history of failure and according to the service manual requires removal of the engine from the frame to replace. Enterprising techs soon discovered that the switch could be replaced in the frame, with a little loosening of engine bolts and prying with levers. Even Honda capitulated and changed the recommended allotment of time in their warranty flat rate manual.
Eventual head gasket failure on this engine is accepted, with the result coolant ingestion by the engine. Replacement factory head gaskets are now pretty much history and aftermarket ones have proven to be much lower quality and unreliable. One aftermarket company that reproduces the composite style Honda head gasket is Cometic in Ohio. Be sure to coat the head gasket with Gaskacinch as experienced Honda mechanics have done for more than a half-century.
Sadly, these bikes are not being appreciated on the vintage market as they should be. That combined with their age means many of them are not being loved the way they deserve.
Bonus tip! It's a great bike, but a GL1000 is not an investment. Every quality part you will ever put into a GL1000 will be diligently sought out over long periods online. And virtually anything you do to this bike will exceed its resale value. This is generally true of most 40-50 year old Hondas. But it is all the more so of this one because the model just hasn't appreciated in dollar value. Maybe this is why so many of these bikes are chopped up these days, turned into "cafe" and "bobber" and similar variations.
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