Vacuum Advance

[Vettefan87]

Vacuum advance

I have a question about the vacuum advance on my bro's distributor. There is vacuum advance on the distributor, but does the vacuum hose run to the carb below, or above the throttle plates. In other words, should the distributor get vacuum advance all the time, or only as the throttle is cracked open. He is having problems with the car (73 Trans Am) running right. I am going to post another thread in the general tech, but he said you guys should be helpful.

Thanks in advance for your replies.


Justin

 

[Vettefan87]

Does the vacuum line for the distributor's vacuum advance go above, or below the throttle plates on the carb. In other words, does the distributor get advance all the time, or just when the throttle plates start cracking open. The car is a 73 Trans Am, with a Q-jet carb.

Thanks

Justin

 

[JohnZ]

Chances are the original setup used "ported" vacuum, with the orifice above the throttle plate, so it got no vacuum advance at idle - that was pretty much the standard "emissions" setup in the early 70's. It will run a lot better if you move the pickup to a full manifold vacuum source (below the throttle plate) so it has full vacuum advance at idle; idle will be more stable, it will run cooler at idle and in traffic, and throttle response will improve.

 

[JohnZ]

See my response to your post in the General Tech Forum.

 

[Vettehead Mikey]

If it's running poorly at speeds above idle, it has nothing to do with being ported or non ported vacuum.

If it's just at idle, try moving the line to the other position. I have no idea which config. is correct for a '73 Trans Am.

 

[vetteboy86]

Thanks guys. I am having problems above idle speeds with it. I do notice that the timing mark advances better with it above the throttle plates if that makes any sense. I am going to play around with it some more now that I know the difference.

Thanks again

Craig

 

[wishuwerehere82]

Below the throttle plate, that way you get advance at idle. Should read 18-20" HG at idle, and drops as soon as you open the throttle.

 

[Bob Chadwick]

Merged off topic thread in C3 section with this thread.