yeah black plug and still ready to soft seize? what oil are you mixing and what ratio...
definitely check into that air leak possibility. out here we run at least 32:1 motul 800 double ester. dont go messing with any of that champion weed wacker stuff. and castrol will foul a plug.
i had that bing and metra set up and it was awight. cracked 50 on it.
what's your gear ratio? also put 3oo miles on that thing before letting it rip...
and that metra will last forever...