7029204 Adjustable Part Throttle Setting

[Greg L.]

I was wondering if someone would happen to know what the proper height of the spring tab should be that sets the power piston height on a 7029204 carb as measured from the contact point to the throttle body.

I finally found a "correct" throttle body assy for my 29204 carb. I say correct because it looks proper and has the correct throttle arm but was told that it is from a 7029215 carb. This has me wondering now if the APT is the same from a automatic or manual car and I'm guessing that they are not.

This one is .020" from the contact point to the gasket surface and is supposedly from the manual version. Mine is for an automatic so I'm wondering if I can leave it as is or if I have to remove the tamper proof plug and adjust it.

Your thoughts are appreciated.

[Mark E.]

Re: 7029204 Adjustable Part Throttle Setting

Greg,

As you mentioned, the APT arm determines the height of the power piston during high vacuum. Its setting is adjusted by a set screw that's hidden behind a plug in the front of the throttle body.

It's a common modification to remove this plug and offers a way to adjust part throttle fuel/air. I've had this done several times and I've heard it's not a difficult job to tackle yourself.

If you have it done, I recommend Cliff Ruffles at Cliff's High Performance.

[James G.]

Re: 7029204 Adjustable Part Throttle Setting

The main difference between an auto and a manual carb is the accelerator pump shot jet is typically larger on the auto.

[Greg L.]

Re: 7029204 Adjustable Part Throttle Setting

Thanks guys but I'll provide a little back ground info to my question.

Years ago I bought an original 29204 (427 auto version) Q-Jet that all checks out as far as the internal component go but the throttle body assy is wrong. I didn't realize this until last fall so I set out to find a correct one. I found one eventually but I'm told that it is from a 7029215 (427 manual version). My parts book list two different part numbers for the throttle body assys for EACH carb number and I'm trying to set the assy that I bought to match my auto carb and was hoping to find the "as delivered, over the counter spec" for the APT adjustment.

I was told that the APT will all vary even on the same carb part number as Rochester adjusted them on each carb but I would think that there would have been a nominal setting for throttle bodies sold over the counter.

Ideally if someone had an original 29204 carb or throttle body assy from one laying around that would be great as I could get a real in service dimension and also confirm the idle screw port size.

[Mark E.]

Re: 7029204 Adjustable Part Throttle Setting

I wouldn't worry about how it was adjusted originally. Set it where your car runs best. It affects air/fuel during high vacuum cruise.