Hot Rods Quadrajet question

I applied the timing tape today and at 3000 RPM with the vacuum advance disconnected I am reading 22 degrees. Is that correct, the vacuum advance needs to be disconnected? I'm skeptical about advancing the timing another 12 degrees to bring it to 34 degrees at 3000 RPM.

 

ok, then try advancing it 6 degrees and see what it does. Did you check the mechanical advance mechanism in the distributor, to make sure it's working right?

 

The mechanical advance does advance when vacuum is applied to it.

 

uh...the mechanical advance is NOT the vacuum advance, it's the thing that makes the timing advance as rpm increases. Weights and springs. On a Chevy distributor, it's just under the rotor. You should be able to turn the rotor clockwise a ways by hand, and it should spring back. It's a good idea to take the rotor off and inspect the advance mechanism, they are known to have problems.

Also, when you see it move to 22 degrees at 3000, what was it at when at idle speed?

short answer, yes it really is supposed to go up to 34 degrees when you rev it up, and vacuum advance is disconnected. If you connect vacuum it will go up to around 50. That seems like a lot, but it's what the engine wants at higher rpm, no load conditions.

 

I set the timing to 30 degrees at 3000 RPM. Now, at idle it is at 15 degrees. The truck has better pick up, no pinging, not any harder to start but is running hotter. It is 90 degrees outside today and while on the road, the trucks engine temperature is is the low 190's and at a stop, goes up to the low 200's which I really don't care for.

 

You can play around with the timing and see where it works best. Some engines like more advance at idle, some don't...usually it is the engines with a bigger can that need more advance at idle, in my experience. You can also play with the advance curve, or see about getting a different distributor, if you want to go to the trouble. If you find a timing setting where you're ok with the performance at different rpm and load conditions, then just leave it there. But you can probably improve it if you want.

 

Jim, sorry I misunderstood your question about the mechanical advance. Yes, both the vacuum advance and the mechanical advance are working.