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i have a 1980 L48, manual transmission, it has no emssions equipment, dynomax sidepipes, a torker intake and an edelbrock 600cfm carb. I put the timming light on, and the mark cannot be found at idle, after searching i noticed it was on the other side (10 o'clock as opposed to 2o'clock). the vaccum advance line made no difference on or off. If i roated the distrubtor to bring the mark to 12degrees BTDC, the car idled fine, but backfired and chocked with any amount of gas. Any ideas??
Are you sure you are on number 1 plug wire. It is the first plug wire on the drivers side. It seems impossible that the timing is off that far. Also when the vacuum line to the distributor is disconnected the timming should back right off and the idle change.
Setting timming is done without the vacuum line on the distributor. Check vacuum in the line and also check if the vacuum advance is working in the dirstributor. With a piece of tubing and sucking with your mouth with the distributor cap off you should see the plate holding the rotor should advance when sucking and go back when you stop sucking.
i am sure it is on the number 1 cylinder, we tried them all anyway, my dad thought it might be a vaccum problem too, but the car has been running for over a year like this, does that make sense?
Slipped balancer, incorrect timing cover or timing tab would be my guess. You need to find TDC on #1 and then verify where your timing mark is reading on the timing tab. Not all SB chevy balancers, timing covers, and timing tabs are interchangable. So if you have a mismatched combo there will be no way to get a correct readiing.
Is the mechanical advance functioning? Set the timing back to where it will take some throttle and watch the marks move are you increase rpm to make sure that it is. If the dist is locked up and not advancing, 12º will be fine at idle but not once rpm is increased. I would also consider what sb69coupe posted a possibility.