rollyman

I recently intalled a Pontiac Q-Jet intake manifold on my 1967 GTO. The manifold was from a 1973 which I was told is the best way to go because this 400 engine has 6X heads and the 73 manifold will achieve proper alignment with the heat crossover port. -- I also purchased a rebuilt Q-jet carburetor. ------------- The car started right up, but does NOT idle smooth at all even after much adjusting time spent. --- Seems to act like it has a vacuum leak which is obvious when I put my hand over the the airhorn to block off some of the air intake the engine idle picks up ---- I have checked EVERY nick and cranny several times and can not find the source of the leak. --- I should point out that this manifold is designed to work in conjunction with an EGR valve which I have removed it and blocked off with a plate which has been installed with sealant.
My question is: Could this be the carburetor? or, should I remove the intake and replace it with another such as a Edelbrock Performer to eliviate my concerns about using a EGR style intake????
Thank you.

 

DaveH

Have you tried squirting a little starter fluid around suspected areas (see if there's a rise in rpm) to help detect a vacuum leak? I don't know of any particular reason that the '73 manifold shouldn't work with your set-up.

lars

If you bought a "rebuilt" Q-Jet, the carb is seriously screwed up. Every "rebuilt" Q-Jet I have worked on has had modifications done that leans it way out. Most common mod is that the rebuilders cut the bottom stop pin off of the power piston, allowing the piston to go to an extreme lean position at idle and light throttle cruise. You need to tear that carb down and do a thorough inspection and setup to make it right - you're going to need some replacement parts to fix the damage done by the "rebuilder"...

rollyman

Thank you, this gives me hope regarding having to tear down the intake which I spent a LOT of time and effort to bring it to a high state of detail.
I have meticulously installed many intakes in the past and NEVER had a vacuum leak. So hopefully its the carb like you have suggested. The rebuilder seems like a responsible guy and I'm sure he will take care of it. Additionally I believe he will welcome your sugesstions and appreciate your expertise. --- Other than the poor idle I should mention the engine has amazing and very crisp throttle response which I would assume has no correlation to bad idle caused from an incorrectly set up carb with a severe lean condition. The car has an MSD distributor and therfore has no vacuum advance leak to enter the picture. Again I very carefully stuffed a rag at the source of any possible air leak with no effect whatsoever which tends to point to the carb for the reasons you stated. ---Again thank you very much and I will keep you posted.

lars

If the rebuilder is an individual and not a commercial carb builder, it may not have the damage and setup problems mentioned in my post above. When you indicated you had procured a "rebuilt" carb I assumed it was from AutoZone, NAPA, or one of the other outlets. But you should still check that carb setup for jeting to spec, correct type of float, correct float level, etc. If you want some interesting reading on Q-Jet problems, you can e-mail me for my "Q-Jet Problems" tech paper:
V8FastCars@msn.com
On a side note, I have run into several stock Pontiac iron intake manifolds that have a twist to them. These twisted manifolds will leak vacuum and never run right. But troubleshooting is easy by just squirting some starter fluid at each of the flange corners.
Lars

wytnyt

allow me to suggest using a less volatile
spray instead of starting fluid,,,,dont ask i know this