Im having a problem with one of my 454's. Last season it was down on rpm. Its very hard to start, cranks fine, but if I pump the throttle say 6-7 times, it will start for about 1 sec and immediatly die, with a big puff of smoke out the flame arrestor. Also, while cranking, for every revolution of the engine cranking I can hear what sounds like air leaking thru the carb. It was like this at the end of last season. Very hard to start the first time of the day. After it was warm, it would start ok. Only backfired thru the carb once and a while while planing off. Timing set at 8 or 10 at the crank.

Could it be a bad valve, or maybe a worn camshaft? Thanks

I'm no engine guru, but my guess would be a wiped lobe on the camshaft. I had it happen in a car and it acted similar to that. Could also be a broken rocker arm....same effect but would be making alot of noise.

do a leak down test will answer all questions, dont think is a cam issue maybe a burnt or sticking valve though

ran a compression test yesterday and had 155-170 on all cylinders except #8, which was 110. maybe a valve problem