Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Quadrajet 7029282 non adjustable APT

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Kavesh:
Btw I like the idea of the screw to control the APT system.

Cliff Ruggles:
The original baseplate was used when the factory set the APT height.

Installing a different one changes all that, sometimes not for the better.

There isn't anything going on with a baseplate that would cause "erratic idle" unless there is a LOT of play at the throttle shaft (vacuum leak).  ALL of those older units need bushings installed anyhow, which would take that out of the equation.  They had too much play brand new and it isn't going to be any better half a Century later!

I would recommend rebuilding the baseplate with bronze bushings and installing an external APT screw at the same time.  This will get rid of any potential issues there and allow for fine tuning in the normal driving range without having to take the carb apart and change metering rods......FWIW....

Kavesh:
So if I understand you Cliff, even though the carb number is the same, when the carbs were put together at the factory, each carb was set up individually and therefore parts should not be interchanged? I shall try the original baseplate again.

The primary shaft bush has a minor play but does not seem to have a vacuum leak. I tried spraying carb cleaner around it and the idle did not change.

Cliff Ruggles:
Side play at the shaft is a vacuum leak.  I haven't seen an early carburetor that didn't need bushings installed for the primary shaft.

In addition to leaking, play in the primary shaft can and will cause idle issues as it may not settle down to exactly the same spot each time it closes.  This may be part of or all of your issues with idling problems......

Kavesh:
Thanks Cliff

The bushing is something I will need to get done.

On a side note....
A kind fellow car enthusiast from the USA had offered to and I accepted to send me some bushings in 2019. He used the US postal service which in turn would use the South African postal service to get it to me. I waited 6 months and went to my post office weekly and tried various call centres to track the package. NO LUCK.

Eventually John messaged me saying that the package found its way back to the USA as it was unclaimed. Its a sad reality here with any government operated business. Nothing works as it should.

So now if I need anything I would need to use a private courier but as you know they are extremely expensive so I hesitate to order just a small low value part.

Thank you again for all your invaluable advice.

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