Q: I have a 1983 Honda CB1100F. The carburetors are overflowing. I have replaced the float needles. I was told the floats were white when new; they are now dark brown. If I replace them will it cure my carb problem? The floats are $65 each, and I wanted a second opinion before I spend that much money. — Mike Gregg/via email
A: Without seeing the floats, I can only guess as to their condition. It depends on the type of float you have. Are they hollow or solid? If they are hollow, the color of your carburetor floats has no effect on how well they work. The important consideration for hollow floats is whether or not they are still sealed, with no fuel inside them weighing them down, which would cause overflowing. If they are sealed, then they should still be working as designed. If the floats are a solid foam type, it’s hard to tell if they are still good without a new set to test against. If you have a new set to test against you can try floating both sets in gasoline and seeing if they both bob to the same height or if the older set sits lower in the fluid. MC
Q: I am in the process of restoring a 1970 Yamaha AT1 125. Can you give me some advice on setting the fuel/air mixture screw on a Mikuni carburetor? — Phill/via email
A: There are two screws to adjust when setting the idle on a carburetor. One adjusts the slide height and is called the idle speed screw, while the other adjusts the air-to-fuel ratio and is called the idle mixture screw. The manual for the AT1 says start the idle mixture screw at 1-1/2 turns counterclockwise from fully screwed in (lightly seated; don’t screw it tight), then adjust either way in 1/2 turn increments to find the fastest, smoothest idle. If the fastest idle is too fast, turn the idle speed screw out to slow it down. Again turn the idle mix screw a 1/2 turn clockwise and counterclockwise seeking the fastest, smoothest speed. Once you determine which direction helps, refine it to 1/4 turns either way to fine-tune the mixture. If you find that the bike stumbles a bit when you open the throttle, 1/4 to 1/2 turn tighter will richen up the mixture a bit and compensate for the added air in the mix from the opening slide. MC
Q: I’m trying to take the gas tank off my 1970 Triumph Bonneville and am having trouble. I want to have the tank and fenders repainted back to original Triumph color specs, as well as rebuild both carburetors. — Jeff Sniadach/Moline, Ill.
A: If it’s the original tank there should only be three nuts/bolts holding it on; one at the rear of the tank under the front of the seat and two up front under the tank. The front nuts may be hidden behind the factory reflectors if those are still on the bike. I don’t have a service manual for that year U.S. model, but looking at the parts book it seems the only access is through the back of the reflector housing with a ring spanner/box wrench. Now I see why you hardly ever find one of these with the reflectors still on it! It may be possible to remove the reflector and access the tank nut from the front. If those three fasteners and the gas lines are removed, the tank should just pull right off, watching to make sure you don’t scratch the paint on the handlebar mounts. Hope this helps. MC
Q: I have a 1981 Honda CB750K with 54,000 miles on it. I took the bike to the Honda dealer to have the carburetors overhauled and was told that the cam chain needed to be replaced, so they did a complete engine overhaul. Four months and many parts problems later, I got the bike back. It runs great but has an oil leak at the drive sprocket. They have put two more seals on and they have both leaked. They glued the second and third seals on. The bike was not leaking oil when I brought it in. Everything is tight. The seal only leaks when the transmission is in gear and the shaft is turning. The people at the Honda shop say they do not have a clue. I was an engineman in the Navy for five years. I have never seen anything like this. — John K. Thompson/via email
A: If you hadn’t mentioned the top end overhaul I would suggest you have a burr on the final drive sprocket that is destroying the seal. Since you mention that the problem only showed up after the overhaul, I’m going to suggest a different cause. I wonder if, during the top end rebuild, somehow the engine breather became blocked? There shouldn’t be much pressure buildup in your engine, but with blow-by from the cylinders plus a little pumping loss it might be enough to produce some internal pressure in the engine. Since the engine and gearbox share an oil supply, the easiest place to relieve this pressure might just be the big seal at the final drive sprocket. Ask the Honda shop to test the engine breather and see if it is still working as designed. There is also the possibility that the automatic chain oiler is doing its job too well. There’s supposed to be a felt element built into the hollow end of the output shaft that is oiled by internal circulation. The drips from that are spun off by centrifugal force to supposedly lubricate the chain. If the felt is missing, or otherwise damaged, I can see where the volume of oil would increase drastically. MC
Setting ignition timing
Q: I plan on installing an electronic ignition in my 1965 Triumph Bonneville this spring, although it’s been running just fine with points. My question deals with setting the timing. The primary cover on this bike does not have a plug/cover to remove so that a timing light can be used. What is the proper method used to set final timing under these conditions? — Rich Reed/Colgate, Wis.
A: Much will depend on the brand of electronic ignition you choose, but you can set static timing using piston position as a reference. Your Bonneville has a maximum advance of 39 degrees before top dead center and the auto advance unit’s range (marked on the back) should be 12 degrees. The usual formula from Triumph for timing was to double the auto advance range and subtract that from the maximum advance. In this case that would be 39-24=15. Fifteen degrees is the static advance setting. Using a table I found in the service manual for your machine, that translates to 0.068in (1.73mm). That is how far before top dead center (TDC) you want the piston when setting the timing. You can use a TDC tool if you have one or — carefully — a piece of stiff wire. Make sure the wire is long enough it won’t fall into the cylinder when the piston drops, and don’t leave it in the cylinder as you rotate the engine: you risk bending the wire or tangling with the valves. Remove the valve adjustment covers on the right cylinder so you can tell when that cylinder is coming up on compression. Rotate the engine with the kickstart, watching the intake valve. Once it opens and closes, the compression stroke is coming up. Put your finger over the spark plug hole and you’ll feel the air being compressed. Insert your measuring wire. Rotate the engine until it’s at TDC on the compression stroke. Find a reference point, insert the wire and mark it at TDC and again at 1.73mm higher than TDC. Roll the engine backward until your mark is at the reference point. Install the electronic ignition pickup. This should get you close enough to get the engine running. Once the engine is running you can use a timing light to check the position of the electronic ignition trigger as it passes the pickup at the engine speed the ignition manufacturer specifies. If you find the timing off slightly, adjust the pickup plate as you would a points plate. MC
Q: I have a 1970 Norton Commando with a fiberglass tank. It is leaking again after sealing the tank a couple of years ago. Do you have any suggestions other than purchasing a new steel tank?
A: Unfortunately, I don’t have any easy fixes to offer. Once the alcohol has found its way under the liner, it will continue to work on dissolving the fiberglass resin. If the liner is Kreem or something similar, it may be possible to dissolve it with MEK (methyl ethyl ketone) and then attempt to reline with a novolac epoxy liner such as Caswell. But even then, there is no guarantee the fiberglass will remain intact. Inexpensive steel tanks are available from India, but reports have been mixed as to quality. There are some modern fiberglass tanks out there that claim alcohol resistance, but I’m still not convinced a fiberglass tank is a safe option. MC
Q: I have just restored a Suzuki T20. The bike will start on the first kick and it idles well, but the right exhaust sputters out oil and gasoline and the right spark plug is fouled, black and oily. The right cylinder makes a popping sound. I tried advancing and retarding the timing, but it didn’t make a difference. I think the problem is the coil for the right cylinder. It has new rebores, pistons and rings. The crankshaft was rebuilt with all new seals, bearings, etc. The battery has a full charge. Another symptom is the compression. With the kick it shows only about 50-60psi on both cylinders. Should it be higher? The specs say 130-135psi, not sure how it can go this high using the kickstart lever? Any ideas would be most appreciated. — Osvaldo Castagna/Australia
A: With a compression reading that low, I have to ask: Did you hold the throttle wide open? You could get a low reading like that if the throttle slides were closed. Holding the throttle open allows the engine to get the full amount of air needed for compression. Your compression must be higher than 50-60psi in reality if the engine is running at all. Try it again, kicking until the gauge indicator stops increasing. As for the right cylinder, make sure the carburetor float isn’t leaking. If it is, it will sink in the float chamber and cause that side to run rich, which would explain the fouled plug. Assuming it’s made of brass, there’s a simple test for a bad float: take it out of the carb and shake it. If you hear fluid sloshing around inside, it’s gone bad. If the right side has been overfed, so to speak, you’ll have to get the engine good and hot to burn out all the excess fuel and oil in the crankcase on that side. You may find your problem takes care of itself after a good long ride. Carry a couple of extra plugs and a wrench, just in case. MC