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Three simple things to ck:
1: Timing, if in doubt retard the timing slightly & see if it helps
2: Fuel mixture. I run a 535 w/ a Holley 750, and I am not jetted to max. Sounds like you are WAY overcarbed! Make a WOT run, shut off & coast to a stop. Pull 1 plug (prefer #4) and ck--if it has raw gas on it or is sooty black, jet way down or go to a smaller carb.
3: Throttle plates. Make sure throttle plates are not binding OPEN on intake--this would cause a rich condition and run-on. Also ck carb for a blown power valve caused by backfire.
I really think you are too big on carb--if you have a smaller one, it might be easier just to bolt it up and see what happens before you grenade the motor from detonation. Good hunting, and please post results/further info, OK??
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"I think we have more machinery of government than is necessary, too many parasites living on the labor of the industrious." Thomas Jefferson
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