any tips on setting vaccum advance

Asked by Mar 11, 2015 at 11:27 PM

Question type: Maintenance & Repair

1980 gmc 2500 tuck 350 ,1406
edelbrock carb ,accel distributor with
adjustable vaccum advance.

2 Answers


That is base entirely on the quality of fuel used, the better fuel the more advance you can get, the adjustments is more of a feel in the way the engine is performing at any given RPM, if you have one of the fancier distributors the breaker wil be marked in degrees, using a vacuum pump you can start with a setting of around 8 degrees at full vacuum, if the distributor is not a degree type then reset the base timing to 0 degrees at a low idle then using the timing light and the vacuum pump pull a full vacuum and check the degree wheel reading it should be around 8 degrees to start, if not adjust the advance to that point, might take a couple of tries to get it, once set then put it all back to specs, and road test, get up to an steady engine speed of around 1800 to 2000 RPM then lightly accelerate and listen for any engine pinging, if you get some then you need to back the advance off a little, use 1/4 turn at a time, if you don't hear any pinging then advance it 1/4 turn at a time until you do, then back it off 1/2 turn and recheck. That's about it but remember fuel is the big thing here, the fuel guys try to tell you that 87 octane stays 87 octane but it don't, around here the quality changes daily at the pumps, I use StaBil Marine additive it at least gives some more stability to today's garbage they call fuel. HTH

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Thank you I appreiate the help greatly

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