Cliff's Quadrajet Parts and Rebuild Kits

General Category => Quadrajet Carb Talk and Tips => Topic started by: Pav8427 on April 17, 2025, 10:57:28 AM

Title: Early non APT primary rod set up.
Post by: Pav8427 on April 17, 2025, 10:57:28 AM

Thinking ahead for a possible build. I have a clean 268 Pontiac carb in my pile. Other than making sure arms are level and straight, is there a start point to shoot for when setting primary metering rod height? Either a dimension or at least a good visual start point? Once in service, can or should you be able to tweek them lower/higher based on performance?

Title: Re: Early non APT primary rod set up.
Post by: Cliff Ruggles on April 26, 2025, 02:06:47 PM

What is the carburetor part number?  Many end in 268?

Title: Re: Early non APT primary rod set up.
Post by: Pav8427 on April 28, 2025, 07:38:26 AM

Duh. Bet that would help a bit.
7029268

Title: Re: Early non APT primary rod set up.
Post by: Cliff Ruggles on May 01, 2025, 02:16:56 AM

If you are using the original style metering rods there isn't much benefit from bending the hanger arms up or down to try to fine tune part throttle A/F.  Most important is to make sure the upper section is well located in the actual orifice of the jets, and that the tips are as well when the power piston is at full height. 

Pretty common for PP hanger arms to be bent, up, down, one up, one down, etc, from previous rebuilds.

I was working on a 1980 Caddy carb yesterday that was just rebuilt and both arms were bent down quite a bit.  It was pretty obvious just looking at the PP that they were not level, but it still was assembled that way by the previous builder.....

Title: Re: Early non APT primary rod set up.
Post by: mcx on May 01, 2025, 03:34:34 AM

Those early Pontiacs don’t have any APT feature to adjust the primary rods depth in their jets …so purchase some washers and install one at a time inside the power piston and spring assembly…it will slightly lift the  primary rods just like a real APT screw…swap out your original primary rods for a set of “B” stamped rods…The “B” have a taper so they have a adjustment range to take advantage of. Only small disadvantage is you have to be careful removing the air lid each time to try an additional washer, though it’s pretty easy stuff on the early carbs.

Title: Re: Early non APT primary rod set up.
Post by: Pav8427 on May 01, 2025, 07:29:41 AM

Thats a new one on me. Would assume that would work for any non APT early units.
Will keep that one in my toolbox as I move forward.

Thanks. Doug

Title: Re: Early non APT primary rod set up.
Post by: jim71400 on June 05, 2025, 12:13:42 AM

I think you can knock out a plug in front of base/throttle plate  and there is screw in there which is an early style of APT adjustment????? Dont think it needs packing??? Could be wrong.

Title: Re: Early non APT primary rod set up.
Post by: Kenth on June 05, 2025, 12:59:02 AM

There is no APT on Pontiac Qjets until the 1975 M4 units, however there is an conical off-idle adjustment screw under the triangular washer on air-horn wich affects the upper idle circuit air-bleeds on 1969 and earlier units and affects the upper main circuit on 1970-74 units.
Changing rods (non-B suffix) and/or jets is the way to tune a Pontiac Quadrajet if needed.
I have found this is seldom needed if the idle circuit is properly modified for todays fuels.
Also, changing main jets/rods will NOT help the idle circuit as the idle circuit is a stand alone circuit with its own jets and airbleeds.

HTH

Title: Re: Early non APT primary rod set up.
Post by: Cliff Ruggles on June 06, 2025, 12:02:50 AM

Correct, jets and metering rod are NOT the correct way to tune the idle system.  Even so I see folks trying to do this.  Just yesterday I took a call from a guy who was clear down to .064" main jets with 44B rods trying to cut-off some idle fuel because his A/F meter showed WAY rich at idle. 

I told him that he needed to look at IFR's and DCR's, plus the IAB's, and that I couldn't help without a carburetor part number or specifics on those items.  I got neither one so moved on to better things......FWIW....