How's it going? I have a 1980 Z28. I was working on the timing. I set the timing to the recommended 8* TDC. When I reconnected the idle advance vacuum line and looked at the timing again, it was well above the 12* mark (guess close to 20*) Is this normal? Or is there a problem in the diaphragm, vacuum line's?

Thanks for the help.

 

9 times out of ten, I've never gotten a change in initial timing, whether the vacuum advance was connected or not. But there can be instances where it can change, if the carb design has a vacuum port in the venturi that's below the throttle blade, or if you need to have the throttle blades cracked open a little to keep an idle up. Or, is your vacuum advance connected to a full manifold vacuum port on the carb, instead of ported? That would do it too.

 

Thanks for the reply. The vacuum line is connected to the carb.

 

The carb has more than one port to connect to. One side is ported/timed vacuum (little to no vacuum at idle), and the other is full manifold vacuum (definite vacuum at idle). What kind of carb do you have, and which side is the advance connected to?

 

Its a stock 4 barrel carb. I did some more reading and research and from my understanding everything is correct.

Thanks for taking the time to help!

 

did you try switching the vacuum hose and see what happens to advance.