Join Date: Mar 2002
Location: Austin, TX, USA
Re: Vacuum advance questions..?
Yes, vacuum advance adds advance at idle. 20* is about right for an idling motor. The 16* base timing sounds like a lot for a motor that developes 14-15inHg of vacuum. That may be where your problem lies. Knock the base timing back to 12* and see if it doesn't run a little better.
I bought a Crane adjustable vacuum advance can with a advance limit. I used my hand vacuum pump to adjust the can to advance fully at the measured idle vacuum (14 inHg in your case). I used the limit adjuster to set 22* idle advance (about 12* over base timing).
68 Coupe, 350 w/ Edelbrock Performer RPM heads, cam, intake, 700R4, Dave's small body HEI