Questioni have a honda sl90,the problem is that the spark plug turns into black & bry in color..the piston and piston rings are new,the mechanic adjusted everything in the carb,we remove the air cleaner in the carb,adjust the contacts,floater,but its the same result.im using a d6hs spark plug. i buy a new carb but its not a genuine,we ccall it a replacement and its almost the same with the original carb and we try to use the old one but its the same result..can you please help me
AnswerPablo, a number of things can cause gas-fouled plugs, including a weak spark (be sure that the battery is new and fully charged), incorrect ignition timing or sticking/frozen spark advancer and incorrect float level settings. There are 4 carb models listed for that bike: SL90A, SL9KA, 571A, 676A. SL90A float setting is listed at 5mm, whereas all the other ones are 21mm. #85 main jet for SL90A carb, #95 for SL9KA and #92 main jet for the 571A/676A carbs. Idle jet size is #35 for SL90A and #38 for the rest of them. Needle clip in #2 slot from the top. Idle mixture screw setting is 1 1/8turn out. If the engine was just rebuilt, recheck the valve clearances, as they can close up during break-in periods. D8HA or D8HS spark plug is normal heat range. If you have changed the air filter and/or the exhaust system, then all the factory settings are probably not going to work now.
A weak condenser or loose condenser connection to the points can cause intermittent spark issues, which lead to fouled plugs. Compression should be 150-180psi. If way low, then the valves are too tight, are leaking or the cam timing is incorrect.
Bill Silver
