It looks like you have already tried all the things that
have been suggested
by the guys responding except for one: The crankshaft
vibration damper.
The outer ring must have rotated slightly giving you late
ignition timing.
My vote goes with those that said that that was the
problem......phil


add another vote for this, check the timing mark on the balancer. Is
the pointer welded or bolted to the front of the motor, I've seen the
wrong one installed on the bolt on type.

BTW, I've never seen or heard of a stock factory damper that was
pinned, maybe a high performace aftermarket, but not an OEM.
Thank You,
Randy

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