vacuum advance question.

[pappabear71]

Hey all. I have a question. I have a Rochester 2 barrel on my 67 Cat and, I have been having problems with the way the car is running. I have changed points, plugs, the usual culprits, even got a new carb for it. Now, here is my question. The vacuum advance, should that be connected to a gradual vacuum or a constant vacuum? I think it is gradual as, the more throttle, the more the advance advances the timing. Right? And on my carb, there is only one port to hook any kind of vacuum too. Now, there was a hole in the front of the new carb with threads the looked like some sort of fitting might be attached where there wasnt one on the old one. Anyone know more about this? Thanks.

 

[Kraig1957]

Plug it into a direct (non-ported) vacuum source. That will give you maximum vacuum advance at idle, when the centrifugal advance is at minimum. When you accelerate the centrifugal advance takes over. The only time I see vacuum advance plugged into a ported source is for emissions control systems.

 

[melsg5]

I agree with Kraig1957 for best idle and cooling you want full vacuum advance at idle.

 

[Kraig1957]

Make sure you don't have the vacuum advance hooked up to the distributor when you finish adjusting your points and then set the timing. I always plug a vacuum gauge into the hose from the non-ported, direct manifold vacuum source. Then when the timing is set to factory specifications, I unplug the vacuum gauge and plug the hose into the distributor vacuum advance.

______________________________

 

[pappabear71]

Ok. Thanks for the help. Turns out, my issues was the springs on the weight under the rotor were shot. Replaced them and the car is running like a top.

 

[melsg5]

good to hear, if you are ever in the distributor again put a drop of 20 weight oil on all the pivot and rubbing areas.

 

[Zimgxp]

The farther the throttle is opened, the less timing you will have. It advances at light load and high vacuum conditions.