Quadrajet question

[Shadizarvan]

Hi Team. Just wondering what this part of my quadrajet is. What does the hose attach to and do I need it. It has been disconnected for the last 20 years.

quaddie.jpg

Cheers,

Max

[axistr]

This vacuum servo is designed to lock out the vacuum secondaries at low manifold vacuum, (during low engine RPM). If the secondaries open to early the engine will run rich and bog down until the engine gains RPM and a higher inlet manifold vacuum. The secondaries will open only a minimal amount at full throttle until the servo has enough vacuum to pull the leaver and unlock the secondaries so they can open 100%.

[Shadizarvan]

Thanks Lenny.
So it should be connected to any manifold vacuum source - not ported?
Cheers,
Max

[axistr]

Memory not as good as it used to be Max, but I think they may have been connected to ported vacuum. Might pay to find a vacuum plumbing diagram for the intended model.

[Innuendo]

Best I can remember is that BS didn't happen until WB and Commodore. HZ didn't have it.
If you can show me pictures on the stamped numbers on the drivers side of the carby I can decode for you.

[axistr]

Thinking about the vacuum connection a bit more, it would have to be connected to a vacuum port that doesn't have direct constant inlet manifold vacuum, or the servo would unlock the secondaries at idle which has a high vacuum situation. The vacuum hose would most likely be connected to a port on the carby. I think all Q-jets had this feature regardless of year and series. Yep Inners is right, Carbys from HZ or WB onwards would have more vacuum ports on the carby and manifold for the start of all the extra pollution regs. HX had some extra pollution bits but also started robbing power with retarding the cam timing.