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Diagnose a Quadrajet carburetor problem / Re: 17085292 Idle Speed
« Last post by Raoul Ross on Today at 08:09:12 PM »
Quote from: tayto on Today at 06:19:27 PM
sounds like an ignition problem. the exhaust making your eyes burn is unburnt fuel, not "rich"

That is next on the To Do list, pull the plugs and look under the cap.  ;D
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Diagnose a Quadrajet carburetor problem / Re: 17085292 Idle Speed
« Last post by tayto on Today at 06:19:27 PM »
sounds like an ignition problem. the exhaust making your eyes burn is unburnt fuel, not "rich"
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Diagnose a Quadrajet carburetor problem / Re: 17085292 Idle Speed
« Last post by Raoul Ross on Today at 02:40:16 PM »
So I was able to do more diagnosis yesterday and found a few things, not the least of which is the primary throttle shaft *is* wobbling in the base plate.

The other thing I found out is, when somebody rebuilt the carb and knocked out the idle mix screw plugs, they went crazy and turned them out... a LOT. It was so rich at idle the exhaust burned your eyes.

So through leaning it out I was able to get the idle speed down. That would probably also explain his hot soak issue. He told me if he didn't restart it after sitting for 10 minutes he'd hafta wait an hour before he could get it to fire up again.

Of course the real issue is the wobbly throttle shaft. Interesting that it still holds 20in of vacuum.
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Quadrajet Carb Talk and Tips / Re: Make the bypass air easily adjustable
« Last post by Kenth on Today at 10:20:32 AM »
Some Quadrajet do not show the transfer slots at idle, like 1972-74 Pontiac Qjets.
Other will show the transfer slots with throttle blades fully closed, like some Chevy M4 units.

Not a big deal, if you need to open the throttle blades more than 1.5 turns on the idle speed screw, add som idle bypass air in small steps accordingly.
You may need to add idle fuel to have control of the idle mixture needles.

HTH
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Diagnose a Quadrajet carburetor problem / Re: Primary rod depth in jet
« Last post by Kenth on Today at 10:07:52 AM »
I have found that the APT is set between 3.5 to 4.5 on various units.
4.0 would be a good starting point before the "tip-in" test at 2200 rpm.
Note: the piston starts rising at 2 turns from seated.

HTH
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Quadrajet Carb Talk and Tips / Make the bypass air easily adjustable
« Last post by spoolboy on Today at 08:46:58 AM »
Is there a way to make the bypass air system easily adjustable via some sort of jets or a screw?

It would be cool to not have to move the throttle plates and uncover the transfer slots to adjust idle speed.
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Diagnose a Quadrajet carburetor problem / Primary rod depth in jet
« Last post by 65malibu on Today at 07:29:20 AM »
Is there a preferred depth to use as a starting point when setting primary needle height? I'm reassembling my #17084226 with 50M needles and #74 jets and was wondering where would be a good bench setting.  Where should the step be located inside the jet when the needle is at its lowest point?
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Diagnose a Quadrajet carburetor problem / Re: Secondary throttle blades curved slightly?
« Last post by Kenth on March 27, 2025, 11:04:19 AM »
Welcome to the Forums!

The throttle blades should be flat.
There is absolutely NO reason for curved or bent blades.
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Diagnose a Quadrajet carburetor problem / Secondary throttle blades curved slightly?
« Last post by spoolboy on March 27, 2025, 08:10:00 AM »
In the carb I'm working on, the secondary throttle plates have a very slight curve to them. They will rock if placed on a flat surface. Is this normal or has someone been in there before me and done this for some reason?
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Quadrajet Carb Talk and Tips / Re: help with 17082224
« Last post by Jeff K on March 27, 2025, 07:09:29 AM »
 Back in the early seventies, I picked up a 64 Pontiac Grand Prix. It had a factory 421 4 bbl (real Carter AFB) with a Roto Hydromatic (Slim Jim).
 The Slim Jim transmission had no stator / torque converter. L was a vertiable ratio 3.03:1 range. Then when it shifted into S (1.58 ratio), it would couple hard with allmost zero slippage. D range was 1:1 and also coupled hard with all most zero slippage.
 The transmission worked well when it felt like it, looking back I think it was tempature sensitive. One time I stayed side by side with a brand new Kawasaki Crazy KZ motor cycle. Don't get my wrong, he beat me but he couldn't loose me..
 
 The only car I can remember from the sixties, that used Ported Spark advance, was was Roto Hydramatic (Slim Jim) equiped 61 to 64 B body Pontiacs with the Trophy Series 389 and 421 engines. If you look at the front, bottom, left corner of the Carter AFB equiped Trophy motors, they had a vacuum outlet for the vacuum advance.
I don't remember if the Tri Power versions came with this feature.
I know the 1958 to 64, four speed Super Hydramatic equiped Bonnevilles and Star Chiefs came with regular manifold vacuum advances. Note that the 4 speed Super Hydramatic transmissions were light years stronger and better performers than the Roto Hydramatics...

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