Some thoughts on holistic GL1000 tuning, titled, Five must-haves for a good running GL1000.
1-Properly serviced carburetors
Obviously the carburetors must be clean, but did you know this includes the idle jet? Many don't even know where the idle jet is, or how to remove it for cleaning and vetting. The idle jet, at just 0.35mm size and due to the size of the engine and the bike's gearing, affects a good portion of the practical operating range of the carburetor, and consequently is the most critical jet. Its outward dimensions are tiny also, making it easy to overlook. And, I always "size" the idle jet, meaning I measure its orifice. Another thing a properly rebuilt carburetor includes is having the correct air bleed jets in place. This can be a challenge as replacements are hard to find on the aftermarket, the ones in kits (ugh!) are usually incorrect, and the jets' correct placement in the carburetor is somewhat non-intuitive. The larger bleed jet goes in the smaller primary main circuit and the smaller one in the larger secondary main circuit. Another thing folks miss in carb rebuilds is the GL1000 has a very unique float setting procedure. Unlike the GL1000 carburetors' cousin the CB450 twin, the float gauge is NOT inserted into the cutouts (notches) in the carburetor casting (body). Doing so will set the floats considerably richer than stock. Also, GL1000 carbs need their pilot (idle mixture) screws set richer than what is intuitive. Though not the best for fuel economy or even the best idle, slightly rich makes up for two things GL1000 carburetors suffer from. By design, the carbs are actually too large for the engine. A fact. Honda shrunk the carbs every few years until even the twin-carbed six-cylinder had tiny carbs. And, in connection with this, these carbs really should have come with an accelerator pump, such as the 1100 got. Making the pilots slightly richer than your ear or an exhaust gas analyzer would indicate will compensate somewhat for these design shortcomings. Finally, as with a handful of other Keihin carb models, the Wing carbs lack an overflow system. Bad thing, this. This means that when the carbs overflow, which all carbs will at least once in a great while, and badly serviced or maintained ones much oftener, you never get any outward overflow indication as you do with say a Honda 750 inline four. Instead, the overflowing fuel goes into the cylinders, where it not only will eventually make its way into the engine oil, but more to the point of our discussion, grossly enrichens the incoming mixture. Aftermarket float valves should be avoided on this basis alone, if not for other reasons. Their unreliable seal results in richer than normal running.
2-Properly serviced ignition
I started in the powersports business a few years before the first GL1000 was introduced. From the beginning then I got a lot of exposure to the model: learning, experiencing, and developing skills on it. I even had one of my customers custom-make me a special dwell meter. And, over the years I installed virtually every kind of aftermarket ignition system available: Martek, Prestolite, Maxi, Gerex, MSD and many more. But in the end, I always came back to the stock system as my preferred ignition. And I emphasize "stock." Not Diachi crap. Once properly set up, the stock point system is more reliable than an aftermarket system, just as powerful, and very low maintenance if initially set up properly. The points don't need replacing any oftener than 10,000 miles if OEM and dressed and checked every 3,000. Even if the ballast resistor is removed, which I did pretty often in those days. But here is my point: in all the years I wrenched on Wings in Honda dealerships, I don't think I knew more than a handful of techs who were capable of properly adjusting the GL1000 ignition. Whether using the split timing method (which all good techs were using within a year of the bike's introduction), the "bombsight" tool, or any other method, most folks just seem to have a lot of trouble with this procedure. And it matters. A lot. This is this engine's Achilles' heel. You also want good spark plug caps. Every GL1000 I have serviced in the past 20 years has had one or both of two very persistent problems. First, high plug cap resistance. The caps should be resistance measued ("ohmed") and replaced if over 10K ohms. OEM spec is actually 5K and on my own vintage Hondas this is what I look for. But 10K is a realistic replacement point. Either way, check 'em. Second, looseness. The caps must be on their wires tight. Part of a regular maintenance service on these bikes is to gently twist the caps to gauge their tightness, and if needed, to unscrew them and after nipping off 1/16" to 1/8" of plug wire, to screw the caps back on.
3-Spec cylinder compression
This may seem like a no-brainer but there is nonethess some confusion about this on user forums. First, I never let a carburetor customer tell me his bike's compression is "good." There is no such setting on a compression gauge. Without numbers, the statement is meaningless. Similarly, I am not impressed when a customer tries to exonerate his low compression by saying "at least they're close together!" In contrast to what many forums seem to promote, having the cylinders close to equal takes a distant back seat to having proper numbers. Second, just that, the numbers are important, very important. If you can't get 150 psi out of your engine, be prepared then to never be completely satisfied with how your carburetors work (or seem to) and really how the engine performs. Don't bother checking compression hot, don't mess around with oil and any other tricks. Just hold the throttle wide open and with a well-charged battery see what you can get. If you get less than 150 it can mean many things and the next stage is to perform a cylinder leakdown test to more closely pinpoint the cause. But even before doing that, I tell my customers to simply loosen the valve clearances slightly, from the stock 0.004" to 0.006". Then retest compression. In most cases you will get a gain and if that is all you ever do about your initially low compression, that's okay. Most of us aren't prepared to overhaul the engine. Or even do a professional valve job. So run with it. It works. And the carbs will work better. Guaranteed.
4-A clean fuel tank
The problem with the Wing fuel tank is it is not easy to remove, which means it will likely not see the service it needs. Get after any rust in your tank. Some folks report good results from in situ reverse electrolysis. Others use one of the modern non-acid solutions. Either way, don't depend on your fuel filter to be your carbs' only defense against rust.
5-Good electrical connections
It should not be a surprise to anyone that 40+ year old motorcycles can have frighteningly bad electrical connections. From one end of the bike to the other, dozens of poor connections add up til you have lost a couple volts or even more! One place you may not have thought about however is the keyswitch. The factory switch does go bad eventually and the aftermarket ones are typically much worse. Do a quick check of your keyswitch by putting a multimeter set for low DC Volts across the red and black contacts. Turn the key ON and note the reading. You want less than 0.2 volts as a reading. The value displayed is the drop, the loss, across the switch. Another common dirty connection is at the engine stop ("kill") switch. Same test. Voltmeter across the black and black/white wires. Key ON, kill switch ON, take a reading. Again, you can allow up to 0.2 volts. More means the switch or its connectors are corroded or dirty. The contacts themselves may be grungy (the kill switch is exposed to atmosphere full tine) or its wire connectors may be dirty. Everyone has heard of folks installing Bosch type relays between their keyswitch and ignition coil. I don't favor that, viewing it as a bandaid fix for otherwise dirty connectors, but to each his own. I have never had to do that to get good electrical continuity.
video of GL1000 in my shophttp://www.goldwingcarbs.com/images/fitch_v2.mov