First, double check the firing order. 1-5-3-6-2-4, clockwise looking down at the distributor rotor. It sounds like one cylinder is firing with a valve open. Tight intake valve clearance or a sticky valve ae also definite possibilities. Check the firing order and adjust the valves before you go into a Phase 10 panic and start throwing parts at it.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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