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I have an early style qjet (73 Buick 455) on a 455 engine with a few minor upgrades (headers, aluminum intake, mild cam). It is a 4 speed car and part throttle cruising is hesitating and bucking. So I am assuming it is running lean at part throttle. The primary rods are “45B” so they are 0.045” cruise diameter with a .026” power tip. I see on this earlier model you can not adjust the APT. Any suggestions for a good size primary rod for this application? Thanks
 

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You can adjust the apt no matter whether it’s found on top of the carb or in the baseplate.
Surging can be caused by too much vac advance too.
Test with vac advance plugged off.
 

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You can adjust the APT on the older carbs, but you can’t easily measure the effect on flow without some advanced tools. It would be a very tedious process because of the disassembly needed to make changes.

Your best initial step may be to install a good wideband AFR gauge so you can watch the AFR under different conditions. I have my Quadrajet adjusted fairly well, but can still see conditions where it goes too lean.

You might also call Cliff Ruggles (cliffshighperformance.com) with your carb number and engine specs, and ask for recommendations on jets and rods.

Bruce
 
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