I just put bored 30 over piston and rings and had the heads renewed with new valves and guides. I bought the parts already refurbished and just installed them. I have put 60 miles on so far. Starts well and in my few initial runs it’s ok but an occasional cough. The part that is puzzling me is the plugs. The rear seems fine but the front is too white for my liking.
I have checked the timing and the line appears near the front side of the hole so I consider it correct. I have done the propane check around the head to manifold connections and they appear tight as well. I think that it’s a manifold leak but my results indicate something else. Any ideas?

 

Replacing the intake seals sounds like a good investment.

 

Intake seals is Never a Bad idea. But, If yer accelerator nozzle is aimed at one cylinder more, that cylinder may get a Darker Plug (raw gas) certainly If yer a Throttle Jockey...or yer bike don't idle...
Turn the accelerator pump Off...check if different at plugs!!