Service
SERVICE
Len Vucci
We welcome your technical questions and comments, and will publish those we think are of interest to our readers. Because of the volume of mail received, we cannot return any personal replies. Please limit your "Service" letters to technical subjects only, and keep them as brief as possible. Send them to: "Service," CYCLE WORLD, 1499 Monrovia Ave., Newport Beach, Calif. 92663.
MISSING GOLD WING
I'm experiencing a low-rpm miss on my 1975 Honda GL 1000, which has about 22,000 miles on the odometer. I've taken it to three dealers for a cure, with no success, and I'm getting very frustrated.
I've taken the carbs apart and cleaned them, and checked the needles and jets and they all look fine. It has a Dyna III electronic ignition on it, and the timing is right on. I've checked all plug wires, caps, etc. and have installed new plugs. Measured compression is 162, 157, 162, 157.
I read somewhere that if a GL has 25,000 miles on it and misses, then the problem was something like the secondary needle. No one seems to know what this could be referring to. Can you help?
Jeff Malby Sonora, Calif.
Some J975 and 1976 Gold Wings were susceptible to a low-speed stumble or hesitation caused by excessively lean carburetion, which has been cured on later models.
Unlike most other carburetors, the C V on the GL1000 has two distinctly separate main jet circuits, a primary and a secondary. The secondary main jet is located conventionally, that is, directly beneath the needle jet. The primary main jet, which could be the cause of your problem, is located slightly closer to the outlet of the carburetor. It contributes to the fuel supply from off-idle to wide-open-throttle carb openings.
In 1975 GL1000 carbs, the primary main jet size was #65; 1976 Gold Wings used a # 62. Better throttle response can be obtained by installing richer primary main jets: # 70for the 1975 GL, and # 68 for the '76 Wing.
Another potential cause for poor lowspeed running is the use of gasoline with a high lead content. Tear downs (by American Honda) of several GLs have revealed a buildup of soft deposits around the valve head which has prevented proper combustion chamber sealing at low rpm. This condition might not be evidenced in a conventional compression check, which, in your case, appears to be normal. (Factory specs list compression at 171 psi, cold.) One would be well advised to use lowor no-lead gas as a preventative measure, as a combustion chamber cleaning does not come cheap. Besides, spark plug life is lengthened as the lead-content of an engine's fuel is decreased.
A word of caution before you undertake any of the previously stated stumble-stoppers. A11 carb hoses must be free from leaks, either at joints or from cracks or abrasions. Make sure that the centrifugal advance mechanism is still functioning properly, as static or low-speed timing checks are simply not adequate.
KAWASAKI POP
I own a Kawasaki Zl, and have installed a 4-into-l exhaust to replace the stock system. I retained the stock main jets, but raised the needles one notch. The conversion works fine, but there is a popping sound during deceleration. The color looks right (tan) on all four plugs, and I have tuned up the engine, but the noise is still present. What should I try next?
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Alan Duranceau Montreal. Canada The noise is most likely caused by incomplete combustion during closed throttle running. A free-flowing exhaust can cause an excessively lean fuel mixture which is not thoroughly burned in the cylinder. The unburned mixture flows into the exhaust header, where, under certain conditions, it is ignited by the successive hot exhaust cycle.
The first step should be to adjust and synchronize the four carbs as closely as possible. (See the carburetor article in our March 1977 issue for procedure.) This may eliminate most of the popping.
Next, if necessary, riehen each of the pilot screws Vs-turn (clockwise) and test for popping. (The idle speed may have to be readjusted. ) This should reduce the noise further, and if so, may be repeated for another Vsturn. Further enrichment can be accomplished by upping pilot jets by one size, but shouldn't be necessary in most cases.
REAR RUBBER REPLACEMENT
I own a 1976 Honda 550F with framemounted fairing, pre-load spacers in the forks, Mulholland SS shocks with 90-120 springs in the rear, and Metzeler tires, 3.2519 and 4.00-18. fore and aft. I am considering installing a 5.10-16 when the rear wears out. What is the anticipated result regarding handling, braking, ride and tire mileage, and will the improvement be worth the expense? I ride about 10.000 miles a year, nearly all of it one-up. The engine is unmodified except for oil cooler and electronic ignition.
As it is now, this bike has excellent handling, but braking is only so-so, ride is good, and tire mileage is about 8000 before baldness sets in. I plan to keep the bike for a few more seasons. Thanks for your help in this. I got the fork pre-load idea from your test of the '77 550F. It was the biggest handling improvement of all, and didn't cost a dime. I used sawed-off bicycle handlebar nubs for l'/s in. spacers.
John Stegman Britt, Iowa Adding profile height and rim size yields a theoretical diameter of 26 in. for the 4.0018, and 26.2 in. for the 5.10-16. Although actual diameters may vary slightly, the two wheel assemblies are very close in this respect. The 5.10-16, however, will produce a considerably larger tire-ground contact area than the 4.00-18. This larger footprint will increase rear wheel traction in most situations—braking, for example—but the improvement might not be as great as one might expect or hope for.
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If you 're the type to push your hike to the limits in corners, the 5.10 might he a disadvantage. Where a 4.00 might give warning that limits of tire adhesion are being approached, the 5.10 may allow the front tire to go away first. In this case better would he worse.
If you are mainly a touring rider, as your letter implies, the 5.10 would probably be advantageous. Its size would provide additional shock-absorbing capabilities without mushiness, improving ride and comfort, especially for occasional two-up riding.
As to whether the improvement is worth the expense to you. well, that's hard for us to say. Add the expense of the 16-in. rim, spokes, lace-up and truing to the tire's increased cost over a 4.00-18 and you 've got quite a sum. If you like the looks of a fat weenie in the rear, that's justification in itself.
Try to find another 550F or middleweight bike owner who's performed such a swap and get his opinion. That would be much better than hypothesizing.
And thanks for the positive feedback re the pre-load fix.
STALLIN' SUZUKI RV
I have a 1974 Suzuki RV 125. which runs fine for about 3A mile, then quits. If I let it idle for a while, it will run for about another Vi mile and quits again. The plug and points have been replaced, and the coil has been checked. I'm stumped.
Also, the brake and taillight bulbs keep blowing out. especially when I flick to high beam. And the speedo and tach lights don't work anymore either.
Your help will be greatly appreciated.
Mark Smith Hanlontown. Iowa
First, make sure the gas tank is venting properly—if you're not sure, loosen the cap and see if the problem disappears. If so, clean or replace the cap.
If that's not the problem, thoroughly clean the petcock and fuel line, and replace the fuel filter if one is present. While you're at it, drain the gas tahk and flush it with gas to remove any debris.
If the problem persists, remove the carburetor and give it a thorough cleaning, especially in the area of the float valve. That should do the trick.
As to the bulb-blowing, do you still have the battery in the bike? A It hough the alternator will still run the lights, the battery acts as a regulator to prevent the voltage from getting too high. Without the battery, a voltage surge, which occurs when you flip between highand low-beams, would blow the other lights out. The headlight filaments, which load down the circuit, would not necessarily burn out, either.
If the battery is still present, make sure the terminals are making good connection, the fuse is good, and the battery itself is serviceable. Clean and tighten all of the electrical connections you find, and your problem should be behind you. R3
CARB ERRATUM
A line was inadvertently dropped from last month's troubleshooting piece, and could be a source of trouble for you, not to mention an embarrassment to us. On page 116, in the carb troubleshooting chart, the third block on the top would have you attempt to start your engine with the spark plug removed. It should have said to replace the plug, then attempt to start the engine.
If your engine did fire without the plug, we'd sure like to hear from you!
