2 vacuum questions

[methos76]

i have a 66 t-bird with a 390 in it with a holley 600 my questions are 1. does the vacuum advance have to be hooked to the side of the carb or can it be hooked up under carb on spacer plate, 2nd question can the transmission vacuum be hooked to manifold port or does it have to be connected under carb. the problem im having with vacuum advance is when I have it connected to the side of the carb and im sitting at a stop light my car will die but when its connected under the carb it doesn't die any help would be appreciated

[jtschug]

1) Yes, your vacuum advance should be connected to the manifold vacuum, not the timed vacuum port on the side of the carb.

2) If the engine dies at idle when the vacuum is connected to the side of the carb, then your initial timing is probably too retarded and you would benefit from some more advance.

[methos76]

so if I advance the timing I can hook it up to the side of the carb is that what your saying or hook to manifold vacuum. I haven't checked the timing lately

[jtschug]

Hook up the advance to manifold vacuum regardless.

The port on the side of the carb provides no vacuum to the advance at idle, so when the advance is hooked to that port it is *not* advancing the spark at idle, thus it is more retarded at idle than it would be when hooked to manifold vacuum. The engine should be advanced enough to idle without vacuum advance. So if it is stalling when hooked to that port, then the initial timing is too far retarded.

[scumdog]

Manifold vacuum for sure!
It retards timing when you plant the gas pedal so no pinging yet advances the timing for more mpg when on a light throttle.

Ported vacuum is a crutch to help with emissions and in my experience wasn't used in the early/mid 60's

[64ZCODE]

Manifold vacuum for sure!
It retards timing when you plant the gas pedal so no pinging yet advances the timing for more mpg when on a light throttle.

Ported vacuum is a crutch to help with emissions and in my experience wasn't used in the early/mid 60's

Yes. I've tried running my '64's vacuum advance on both manifold and ported vacuum, and the engine has better throttle response when using manifold vacuum. More advance is needed to combust the air/fuel mix when the engine is running lean, i.e. when idling and when cruising at speed with minimum throttle, and those two conditions are when manifold vacuum, not ported vacuum, is highest.