q-jet vacuum question

[Vette79]

Ports at the very bottom of the carb are full manifold vacuum right?

 

[Johan]

Ports at the very bottom of the carb are full manifold vacuum right?

We probably have different versions of the Q-jet, but my ported vacuum port is actually lower than the full manifold vacuum I now use for the distributor.

The best and simplest you can do is just to disconnect a hose and put your finger at the port. If you have vacuum at idle, it is full manifold.

 

[will1934]

Ported vacuum is an emission era crutch. A motor at idle needs more advance to idle good and stay cool. Lack of advance at idle causes it to run hotter and cuts down on oxides of nitrogen emission. If you conect your vacuum advance can to full manifold vacuum your motor will idle smoother and run cooler in heavy crawling freeway traffic. Set your initial advance to 10 to 12 degrees advanced and the vacuum advance will add 8 to 10 more and your motor will love you for it.