Rochester question

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Dec 23, 2004 | 12:37 PM

sedowney

Thread Starter

Racer

Joined: Oct 2004

Posts: 413

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From: Cohutta GA

Rochester question

I am, with major help from my father-in-law, currently restoring a 73 coupe, and I now know why people buy already restored vettes

. Any way there is a hollow tube about the size of a pencil near the front of the carb that takes a "d" shaped driver.
My question is what does it adjust? and where can I find one of those drivers?

Dec 23, 2004 | 01:58 PM

Boofers

Drifting

Joined: Nov 2002

Posts: 1,665

Likes: 1

From: Ontario

Quote:

...and I now know why people buy already restored vettes

Indeed it can be quite a challenge at times!

This is a guess of course but it sounds like you are referring to the power piston lower stop. This adjusts how far your primary rods sit in the jets when the engine has high vacuum (idle & cruise). The further the rods sit in the jets the leaner your air/fuel mixture is at idle and cruise. There is usually a metal plug over this hole in the bowl cover assembly, a common thing to do is drill & tap this plug for easy removal without having to remove the entire bowl cover.

Clockwise lowers, if you adjust this do so in 1/4 turns then see how it has changed your engine performance. Don't lose your starting point so you can always go back if you have to. You can't really see the lower stop in the diagram below because it is built into the main body.

Not sure what you mean by a "d" shaped driver, I just use thin needle nose pliers to adjust it.

QJet exploded view

This may be of interest to you as well. At the very least read anything written by 'Lars'

carb links

Last edited by Boofers; Dec 23, 2004 at 02:00 PM.

Dec 23, 2004 | 02:03 PM

lars

Tech Contributor

Joined: Aug 1999

Posts: 14,380

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From: At my Bar drinking and wrenching in Lafayette Colorado

That doesn't sound familiar.... can you describe this a little better with the exact location: is the tube sticking out the top of the carb at the front, or out the front of the carb? The only tube sticking out the top front of the carb is the bowl vent tube, and there is no adjustment on or in it. The Q-Jet only has the mixture screws as adjustments, and these are not in a tube. You can also adjust power piston stop height, but again, this is not in a tube...

Dec 23, 2004 | 06:20 PM

PRNDL

Team Owner

Joined: Jul 1999

Posts: 26,545

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From: Huntersville NC

Maybe a previous owner got really mad at the carb and stabbed it with a pencil? This has been known to happen, but usually they hit it with a hammer!

A pic helps a lot!!

Dec 24, 2004 | 12:34 AM

Mr Fanuc

Instructor

Joined: Oct 2004

Posts: 173

Likes: 0

From: Hattiesburg MS

Quote:

Originally Posted by sedowney

I am, with major help from my father-in-law, currently restoring a 73 coupe, and I now know why people buy already restored vettes

. Any way there is a hollow tube about the size of a pencil near the front of the carb that takes a "d" shaped driver.
My question is what does it adjust? and where can I find one of those drivers?

I have my Q jet off rebuilding it right now. Went and looked at the air horn to see if I could find what your talking about. Mine is a '77 but has what I think you are talking about. Is this tube under a small kinda triangular plate with 1 screw holding the plate down. If so, it is the air vent valve. Mine does not have the valve, not all Q jets did. But my casting is set up for it anyway. I don't know what it does, since mine doesn't use it but someone on the forum may have one that does use it and can give you better info.

Dec 24, 2004 | 12:24 PM

sedowney

Thread Starter

Racer

Joined: Oct 2004

Posts: 413

Likes: 0

From: Cohutta GA

Thanks to all who responded. This car has driven me crazy at times, but I am having fun.
Sorry for no pics, I will try to do in the future.
The link that Boofers supplied is great. In that link the tube is on the
bowl assembly cover, and sits under the #15 in that pic.
I love this forum, and find it very informative. Thanks again
Merry Christmas to all.