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Message: <blockquote data-quote="GREG@SN95" data-source="post: 822064">I bought a truck recently, a 91 f150 4x4 with a 302 and an m5od trans.. It was misfiring pretty bad when I got it, I didn't care though since I have several 302s laying around... Long story short, the knuckle head that owned the car before me must not known how to drive a stick... All the pushrods were bent and I think he over revved the thing... Long story short, I got a screaming deal on a mercruiser 351 small block. This thing has under 100 hours, cast iron everything, stainless head gaskets, marine cam and double roller timing chain... Casting numbers read E6T so its an 86 truck motor. The fuel mechanical fuel pump is new, as is the vac advance points distributor, and coil. I set the timing at 10 degrees before TDC (with the advance disconnected). I have the advance hooked straight to the metered vac port (no check valve). I solved a few issues after spending 5 hours learning about metered vac vs manifold vac and check valves and timing etc etc etc...Now the carb is the only thing that isn't new. Its a 670cfm holley street avenger that I bought on ebay 2 years ago. It sat on a shelf for 2 years. The squirters on it were clogged and I halfway rebuilt the carb... I say halfway because the kit didn't come with a diaphragm or any thing else for the secondaries, just gaskets for the bowl.Truck runs GREAT 99% of the time... Here is where it gets weird. Sometimes, while accelerating at like 5-10% throttle the motor bogs and backfires. Sometimes it doesn't. Last night it was running great... Then all the sudden it started running like shit. I thought it had a vacuum leak... But it did not. An hour later I start the truck and its fine...What the fuck could cause this?</blockquote>