Hello, Reading from a "motors" manual:
Centrifugal advance
"0"degrees @ 450rpm-"15"degrees@1600rpm
Vacuum advance
6in of vacuum required to start plunger
max. advance--10 degrees @ 14 in of vacuum
I think i have a "GM" manual and I will check the specs. in it for you.
I am begining to think you have a leaking intake manifold gasket. Check the alingment between the exhaust and intake manifolds to the head with you gasket combination. I am not sure if I typed that understandable. I can scan in a diagram and e-mail it to you, if you want. I have seen some intakes leaking the will not show up at idle(Spraying with solvent or water test).Also you may trying using a small spray bottle of water to spray the spark plug wires at the dist. and at the head. Do both these test at idle and with the motor reved to 2000 rpm. May this will help---Paul
