Author Topic: APT Screw Missing Should I Replace it in Rebuild ?  (Read 1885 times)

Offline 79 4.9 TA

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APT Screw Missing Should I Replace it in Rebuild ?
« on: December 19, 2014, 12:58:09 PM »
Hi everyone, I was hoping someone could help me out.  This is the first time I am ever attempting to rebuild a carburetor.  I have just finished disassembling it and I am currently cleaning it.  The reason I am doing the rebuild is because of a bog when I stomp on or if I am aggressive on the pedal.  I was told it could be the accelerator pump and was advised to rebuild the q-jet.

After breaking the carburetor down I noticed it has been taken apart before, the well plugs have epoxy on them and the APT screw is missing.  The power piston has the metal pin sticking out from it so I believe this unit did have the APT system in it. 

I have only owned the car for about 8 months so far, from looking at the carb it has not been rebuilt recently or was taken apart and then put back together and not cleaned.

From reading allot of the other posts the issue could possibly be fixed by adjusting the APT (if one existed) or possibly some other adjustments.

When I order the rebuild kit from Cliff should I also order the APT screw? 
Should I also order the HP rebuild kit or the standard kit?

Any help is greatly appreciated!

1979 Trans AM
4.9 Engine I believe all stock
Engine runs nice at idle, cruising and passing (except for bog that recovers)
Q-Jet numbers = 17059272

Offline Cliff Ruggles

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Re: APT Screw Missing Should I Replace it in Rebuild ?
« Reply #1 on: December 20, 2014, 03:16:31 AM »
The APT screw needs to be there, but it is not causing problems when you go heavy on the throttle.  The APT screw precisely controls the height of the metering rods in the jets at light throttle cruising.  Since the power piston moves up when you go heavy/full throttle, it is not a player there.

I would replace the APT screw and install a removable set screw in the airhorn for easy access, we can supply those parts when you order the kit...tks...Cliff

Offline 79 4.9 TA

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Re: APT Screw Missing Should I Replace it in Rebuild ?
« Reply #2 on: December 20, 2014, 06:49:36 AM »
Cliff,  thank you for the fast response and information.  I submitted the form on-line and I am ready to purchase the parts once you reply to the form.  Again thank you very much!