Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

1975 Quadrajet APT adjustment 7045222

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dmruschell:
I popped off the plug above the APT adjustment and 1/2 turn counter-clockwise seemed to eliminate the lean surge I was having.

I have smaller rods and larger jets on the way if I eventually need them.

Right now, this horrible carb runs better than any other carb I've put on it, and is preferable to an EFI system I tried out lol.

Is there any way to convert these carbs to use the later style APT? My rebuilder modified it to have a 77-79 style bowl vent because the casting provisions were all there, so the casting itself couldn't be that different. Since it's working correctly now, I probably won't bother, but it would satisfy my curiosity and maybe help someone else who has one of these carbs.

Cliff Ruggles:
Yes, they convert to the later style.  You have to thread the hole for the APT screw, and put a "slot" in there for the later APT style power piston with the pin on it.

Keep in mind here than many of those had an auxiliary power piston in the front hole and single rod on it with a single jet in the main casting (those are really horrible) that will need to be blocked off for the conversion.

This still does NOT eliminate the cross-connecting passages between the main jets from the early APT system, which I am not very fond of and have seen quite a few of those units that simply don't work well no matter how much time you spend on them.

The early APT system is actually quite flawed, as it adds fuel under the jets, which will effect not only part throttle A/F, but everywhere else as well.

It's just a poor design all the way around, however, if you spend enough time with one and arm yourself with enough jets and metering rods you can usually come up with a pretty good end result.

As stated earlier, I typically avoid those units, as the later APT design is far superior in every respect, and far less labor intensive when custom tuning.........Cliff

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