Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Quadrajet Throttle Body Swap - Will it work?
Kenth:
I have managed to loosen of maybe 1 out of 10 APT screws in the throttle plates with the help of various sprays and heating with, among other things, a butane torch.
Nowadays I don't even bother trying.
If the carburetor needs jets or main air bleeds replaced, it will show up during the tip-in test.
DJD OLDS 4MC:
Hi Kenth
We appreciate the advice you shared a couple of months back about swapping throttle bodies on a Quadrajet to accommodate vapor cannister purge. As a follow up to you APT screw removal suggestion, today we successfully drilled out an APT screw without ruining the threads in the throttle body after spending weeks without any luck soaking, heating and trying to gently break the little screw threads free. So far we’re 1:1 in the APT screw removal challenge - two more throttle bodies to go!
My son and I are hoping you have a few moments to spare to look at the attachments we’ve included.
We’re looking for any suggestions you may have for improving a 4MC Quadrajet before we install it and road test it in a 1980 Olds Cutlass Supreme that my son and I have been building for the past few years.
The first attachment lists the specifications for the engine, induction, exhaust and driveline for the car.
The second attachment lists the current and original specifications for the 7040251 Quadrajet we plan to install on the engine next month.
The Quadrajet was modified following suggestions from Cliff Ruggles book a few years back. The current carb specs, as well as the original specs before it was modified are listed.
Based on an Innovate O2 sensor setup we installed on the engine last year, it appears the BB Olds will run at about 13:1 with #69 main jets and #39B primary rods cruising at 18" vacuum, and almost the same 13:1 with 7" vacuum and the power system engaged. With #70 jets installed, it ran a tad richer into the mid-12s, especially with the power system engaged.
When you have time, could you please take a look at those carb specs and advise us as to any changes you feel will improve the Quadrajet before we install it and begin road testing.
Thanks very much.
DJ and Jed
Cliff Ruggles:
The key to removing stuck APT screws is heat, patience and a custom made screwdriver that fits tight in the screw. It may take several "sessions" heating and applying penetrating oil but I'm close to 100 percent in getting them out.
I just removed one from a 1971 Olds couple of days ago that took three attempts to get it out. It actually starting moving a little back and forth on the first attempt, but I had to let it completely cool down and apply more oil, then do the process two more times before it would come out.
When swapping TB's on those units you are going to get much better results with a work APT system when it come time to dial in the tune on the primary side.....
DJD OLDS 4MC:
Thanks for your advice.
So far, I'm 2 for 2.
However, I had to drill one of them out because the slot in the screw got buggered.
I've got a third throttle body soaking, but the screw slot feels like it's buggered too.
Another candidate for drilling!
Attached, please find a copy of the successful workflow I followed that seems to be effective in removing a buggered seized APT screw.
Hope it helps someone out there.
DJD OLDS 4MC
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