Did you read/understand my previous post in your message box? Not being rude, just asking if you need clarification. I went after the most likely reasons 1st. Assuming OEM type ignition,there are at least 5 reasons; 1) vacuum advance hose hooked up to wrong port, 2) throttle blades too far open, 3) bad timing chain, 4)excessive endplay in dist or cam, 5) polarity of magnetic pick-up. Listed in order of most likely, to least likely.Hope this helps. PS; I suppose you could theoretically add 6) rotten harmonic balancer, but Ive never seen one do that.