1965 harley davidson servi-car rear cylinder spark plug is fouling out with black dry soot front spark plug is fine what can be causing this problem and how can i correct it i have tried to adjust the carburetor so its not running rich but still have the problem any help would be appreciated.

 

I would start by checking the manifold seals (the front one in particular) If the front plug looks good and the rear looks sooty it could be you over compensated the idle mixture screw to satisfy the front cylinder because of a leak and the rear is fine making it run rich on the rear cylinder......

 

Is the compression the same in both cylinders? Very well could just the hotter back cylinder just has cooked the intake valve seal and a little oil is running into the cylinder. My guess if it's fouling the plug and making it misfire, then it's probably not that rich with fuel because if it was, it would run like crap.

Oil does not burn, it's just cooked from engine heat. The term, pumping oil is really more appropriate then burning oil. Not sure when the engine was rebuilt but it can actually have close compression and the oil control ring in the back is stuck and complicated by a leaking valve seal.

 

Checking compression would be a good idea but I don't think there's a valve seal issue seeing those older heads didn't have valve seals unless somebody machine them and put them in. Also the OP noted dry soot on the rear plug....

 

My bad..I was think 45 but 1965. Thought surely OHV. But I was wrong. That is the same flathead engine that is in the 1940...

I actually have a 1940-1958 Service manual on that antique.

 

police depts. and hardware stores were still buying 45 inch flathead trikes until 1973 from Harley New and they became electric start before the big twin in 1964