Set timing with timing light but when cruising at about 65 to 75mph the crank becomes noisy and timing seems as though its retarding. but as soon as i continue accelerating crank noise disappears until i keep constant speed.
by 
blazerick
ANSWERS: 2
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first of all what noise are you hearing? If it souns like a pinging noise your timing is too far advanced and or your fuel grade is insufficient, or fuel pressure is too low, or vacuum leak. what kind of vehicle also, because there are a lot that you have to unplug a wire(s) off the distributor to correctly set the base timing.
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It sounds like an older engine and a cracked rotor or misadjusted or struck centifugal advance. The vacuum advance during acceleration is masking it. Try a lower gear at lower speed aty the same RPM to avoid getting a ticket while you sort it out.
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