of erratic timing.

I went to check my timing today because of a miss at idle and the timing mark is jumping back and forth.

Worn chain? Vacuum leak? something else?

87 b150 /6 manual trans

.....thatll be yer chain....

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Yeah....Im the one who destroyed this rare, vintage automobile.....

The chain is a likely culprit, but so is the spring set up on your cetrifigal advance. If one of the springs is weak, it can bounce around when it is all the way contracted. When you rotate the inner plate assenby to make it advance, it should spring back firmly. If there is a degree or two of loose play there, this will cause your symptoms also.

Sam

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True as far as it goes, though an '87 likely has a non-advancing distributor with electronic (computerised) spark control.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks for all the input.

I checked it again today and the timing mark is steady as can be.

Hopefully its just a wiring issue I need to track down.