yes when i fire up my thing the engine ideal but it is only when i rev it it wont ideal any more what do u think it can be i think it might be something with the valves it pops and black smoke come out of it when ou jump on it not a lot but jsut a tiny stream jsut noticable but am i right with the valves needing to be ajusted it is a stock 1973 thing except it has a compufire disxi ignition on it thanks