Questioni just bought this bike the other day, my first bike with more than one cylinder, and i'm having some problems with the left cylinder. it keeps fouling plugs, after about 15-20 minutes of running. i ride mopeds, and usually when a plug is fouled, i clean it off and it'll run again. but with these, no amount of cleaning, or sanding the electrodes will make the plug work again. i've tried these fouled plugs in the right cylinder, and they won't fire there either, so that reassures me that there's nothing shorted in the left cylinder's electrical. the plug is dark brown, but isn't oily at all. it seems weird to me that it would only happen in one cylinder.
thanks in advance,
-chad
AnswerChad, dark brown plugs often are due to oil being burned on them. Excessive oil in the cylinders can be due to broken or worn rings, valve stem seals that have failed, worn pistons and worn valve guides.
First thing to do is to get the compression checked to see what you have to work with. Compression readings should be in the area of about 175 psi.
If compression is low on that side only, you can try to see if the valve clearances are too tight. Clearance is .002" COLD on the compression stroke (valves closed) when the crankshaft marks are aligned with the T mark on the flywheel.
You can also check the spark plug cap for high resistance. Should be about the same on both, in the range of 5k ohms, once you have unscrewed them from the plug wire.
If the plug was fuel fouling (black) that could be from carburetion issues, like float level, main jet size, needle position or idle mixture screw setting. When both cylinders fuel foul, it is often due to the carb slides being swapped from one side to the other. They are L & R specific.
Check point gap at .014-016" maximum, then set the plate so they just open at the F mark alignment on the rotor.
If compression is low and you see some blue smoke from the exhaust pipe, then you will probably need to go into the motor for a top end repair.
Bill Silver
