72 vacum advance base 350 200 H.P.

[Gary L.]

I need help getting my vacum advance back where it should be on the right vacum port on my qaudrajet.Should it be hooked to the front port on the driver side above the idle mixture screw or should it be hooked up to the vacum port that sticks out through the choke area. And I don't know if it should be hooked up to full vacum at idle for timing or vacum under acceleration. The biggest thing I don't understand is how it should affect my vacum advance at idle after I set my timing with it plugged off and then hook it back up to my distributor. Right now I have it hooked up to the port in the front of the carburetor and their is no vacum on that port when idling.Much thanks for all help.

[Rich W.]

Re: 72 vacum advance base 350 200 H.P.

Oh boy here we go..you asked the question about timing..sounds like you have it hooked up to the stock port on the drivers side of the carb..AFAIK that's the stock way of running it..on a 69..not sure on a 72..the vacuum advance is designed to add advance when you load the engine..like going up a hill..but..its not always and doesn't have to be used that way..there are many posts on many sites on how you can hook it up..I dont want to open that can of worms.. hope this helps..

[Joe L.]

Re: 72 vacum advance base 350 200 H.P.

I need help getting my vacum advance back where it should be on the right vacum port on my qaudrajet.Should it be hooked to the front port on the driver side above the idle mixture screw or should it be hooked up to the vacum port that sticks out through the choke area. And I don't know if it should be hooked up to full vacum at idle for timing or vacum under acceleration. The biggest thing I don't understand is how it should affect my vacum advance at idle after I set my timing with it plugged off and then hook it back up to my distributor. Right now I have it hooked up to the port in the front of the carburetor and their is no vacum on that port when idling.Much thanks for all help.

Gary------


The best advice I can give you with respect to the original hose configuration is to check out Dr. Rebuild's catalog. After all, a "picture" is worth a 1000 words. He has EXCELLENT diagrams of just about every Corvette application. The catalog is available online.

[Patrick H.]

Re: 72 vacum advance base 350 200 H.P.

Hope the picture helps.

Follow the link in my signature below if you have additional questions.

[Duke W.]

Re: 72 vacum advance base 350 200 H.P.

the vacuum advance is designed to add advance when you load the engine..like going up a hill
hope this helps..

No, you have it backwards. Load increase is represented by decreasing manifold vacuum, and the vacuum advance reduces advance as manifold vacuum decreases due to increased load such as going up a hill.

Duke

[Stuart F.]

Re: 72 vacum advance base 350 200 H.P.

If you connect to the correct port on your 72 QJ, as the pictures and diagrams will show, that is a ported vacuum signal the source of which is above the throttle butterfly at idle and you won't have any vacuum signal. This internal port connects to a chamber in the casting which can be drilled into at a point below the butterfly in order to give you vacuum at idle. You then have the best of both worlds in that it will look stock yet give you a vacuum signal at idle. This is a modification I made many times back in the day (1972).

The second modification involves the transmission controlled solenoid (TCS) in the vacuum line to the distributor. As I recall, it opens to allow the vacuum signal a certain amount of seconds after the transmission shifts into top gear. I used to run a manual switch control (located under my dash) from a second 12v ignition switched source to activate the solenoid at a time of my choosing. Again, it looked stock for judging and can be switched OFF for an emissions test, or switched ON for improved performance and gas mileage.

I would never recommend anyone do that now in States where they have a penalty for defeated emissions devices.

Stu Fox

[Gary L.]

Re: 72 vacum advance base 350 200 H.P.

Hey Duke,how much vacum should I have at the port to my advance unit when it is sitting at ldle. I always set my timing first,then hook my distributor back up. That was one of the reasons I asked this question,because the way I have it hooked up now,there is no vacum at all to my distributor at idle.Thanks.

[Stuart F.]

Re: 72 vacum advance base 350 200 H.P.

Gary;

If all you want to do is find out how much vacuum you have at a ported connection on your QJ, hook up your vacuum gauge to that port and, if it is ported and shows no vacuum at idle, advance and hold the throttle an amount until you get a steady reading. A full vacuum port should register somewhere around 20" hg.

Please disregard my previous post #6. You're not ready for that.

Stu Fox

[Gary L.]

Re: 72 vacum advance base 350 200 H.P.

Thanks everyone for the great info.