Quadrajet Problem Solving > Quadrajet Parts and Numbers

78 chevy carb

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429bbf:
shark do you pound restrictors in both sets of mabs or can you tune them the way they are? i already bought parts from cliff and i ordered 4 extra restitors.it has 72 jets with 53m rods.this carbs a wreck. i know why the guy gave it to me to rebuild.all the screws were broke off in the throttle shaft, you could throw a cat threw the bushings,throttle shaft bent,g hanger bent over .100   power piston hanger bent . secondary plastic piece broke, and lo and behold he paid somebody a year ago for this great job.its going on a 350 with a small cam dont know any specs.

429bbf:
dont you guys think 77 jets are  to big to start with?

Shark Racer:
If you're running the stock MABs you should stick with a 77. These carbs ran a 52 or 53k, not M. Are you sure it's an M rod?

If you switch out to 070 MABs top and bottom (I did), 72 should be OK. My 17058228 is running 70/70 MAB, 73 jets 44(K? J?) rods.

What's the CR?

I have a mild_ish_ cam and had to go up quite a bit on the idle circuit to keep it from being lean. But my engine has a very low static CR.

429bbf:
thanks for reply. the 50+ eyes have a hard time with them small letters. they are 53M .something id like to know . do the carbs perform the same with large mabs and large jets compare to resizing the mabs and running smaller jets ?ive never taken the same carb and ran it both ways on the same vehicle.most of the info i get when someone wants a carb built is it runs like crap.no other info on cr.heads.cam.gear ratio etc.

Shark Racer:
The M rods are gonna severely hamper performance when getting into the throttle (passing, pulling hills or WOT). Just going back to the stock config should help a bit.

If the car has a more aggressive cam, the idle circuit will need some attention.

Between the bushings, secondary cam, bent power piston rods, and wrong primary rods the carb has a lot of rreasons to run bad.

Bring it back to the stock config and repair all the faults and it should be a night and day difference.

I know Cliff would recommend going to the 70/70 setup. I believe that the fuel curve becomes more predictable with that. In stock config my 17058228 was pretty lean at light throttle and cruise, and horribly rich when the secondaries opened up. (with a pretty significant bog as they opened up to boot :) )

I'd love it if Cliff(or someone else) could explain the effects the air bleeds have on the fueling curve. I think I understand most of the systems now but this is one that I'm still not 100% sure on. I understand that it's emulsion air and more bleed = leaner mixture. My question is more along the lines of "What will be different between a 70 bleed and a 125 bleed if the jets/rods have been changed to compensate?"

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