Vacuum Ports on a Q-Jet
Thread Starter
Racer
Joined: Apr 2006
Posts: 340
Likes: 0
From: Warrensburg MO
Vacuum Ports on a Q-Jet
I have brought up this issue before, but the more I work with the Q-Jet, the more questions I have. Just trying to understand the vacuum ports. For example, the vacuum port for the primary vacuum break is just about in the middle of the carb, but it has constant vacuum. (at least mine does). It seems that with its placement, it would be ported vacuum. Is there any type of picture that shows what ports are ported vacuum, and which are manifold vacuum? Thanks for your help as always. Cheers..
Tommy
Tommy
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,114
From: Crossville TN
You can't tell, just by the location of the port on the carb casting, whether the feed passage on the inside of the carb is above or below the throttle plates. The ports are not necessarily 'fed' by a direct drilled hole. The best way to tell whether you have "timed" (ported) vacuum or "direct" (manifold) vacuum is to take the line off of a port and put a piece of paper across the port to see if vacuum is present [or not] at idle.
