4 stroke rich idle?

Sep 5, 2000
I bought a used XR100 that ran OK but would accumulate carbon on the plug and then run poorly. The carb has been cleaned multiple times and all passages appear open. The float and float needle were replaced. It also has a leaner main and pilot jet (one step leaner was the leanest available) The choke is of the butterfly type not the enricher type. The points and timing are set correctly. The plug is one step hotter (CR6HSA). The plug cap was replaced. The idle mixture screw appears to function normally. I thought it was cured but notice if it is left to idle for 10 minutes the plug accumulates carbon. I tried adjusting the float to lower the fuel level by 0.050”. A short test suggests that the idle is now “clean” but there is major bog and even stall at high throttle openings. (even with the stock main jet) Is there something else that can cause or mimic this condition? (carbon on plug from idling) What is a “weak” coil like?