Been having this problem for awhile. The motor was stroked out with s+s flywheel a new s+s carb.The plugs are 3-4 harley plugs. They last about a 100 miles or so and foul out. When they are pulled they are totally black. Any suggestions to correct this problem. Thanks

 

to big of a main jet -- float not set right flooding engine -bad coil - air leak and over jetted to fix it -- timing -- dirty air cleaner - might help if ya say what size the engine is.. if ya solve the problem THE best plugs are the autolite XS65 if they are long reach -- i have welded aluminum bungs where the original short reach plugs go to convert them to long reach -- even when i dual plug heads i make them both long reach -- i would check the float level & see if the needle leaks first -- then the jet size-- a stroker with 4.500 stroke 84" in an S&S carb should be 72/74 main -- 88" 74/76 -- 93" 76/78 -- BUT it depends on your altitude sea level or over 5000' mufflers or none .

 

After trying that switch plug brands. My Shovel never liked HD or Champion plugs.

 

The motor is a 88" with a 72 main jet. Not sure about the float but if it is leaking by the carb should be leaking, which it is not. Will check the coil and there is no air leaks. Will update findings.

 

the needle in the bowl (float needle) may not be seating and flooding the engine-- if thats the bike in the pic 88" you need a better flowing exhaust--- what cam is in it?
88" S&S 3 5/8th cylinders?? 4.250 stroke -- a sifton 468S would work really well