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I just built a 454 chevy engine for my motorhome. It idles well, and everything is new, dist, carb, hyd roller cam, plug wires ect. It has 9.1 comp ratio, and a alum intake. The problem is when I get the engine in a hard pull it will sometimes backfire, if you let off just alittle it will run fine. I have checked everything. I am thinking it has something to do with valve adj or cam timing.
Any possibility are you getting crossfire-#5,#7,vacuum to the advance -wrong-should be -o- at idle---16+ at up throttle.
or is the exhaust to tight for the rebuild---to much restriction.?
A lean mixture will do the same thing-.is the fuel tank vent clear and NOT stopped up-? I had that happen once--mud dauber had a home in the vent'
and do change the fuel filter too..
rich.
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