Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Rebuilt Carb, all bog except idle
Cliff Ruggles:
Fuel level and float settings are directly related to fuel pressure. Most late model fuel pumps had high pressure, and they used a return system to keep fuel in circulation. This accounts for the lower float settings listed in the build specs for many later units.
"Bog" is most often a lean condition. If you have a large MAB carburetor, this is not uncommon even with huge jets and small metering rods in them.
Timing is equally as important as fuel delivery. If the ignition timing isn't enough for the engine it can't burn a lean mixture and a "bog" or lack or power will result......Cliff
Kjetil:
Thanks Cliff.
It is a MAB carbuertor, but I thought your choice of jets (77) and rods(44) for the setup would account for it. I did order air bleed inserts from you as well. Would it be possible to size them so I still can run the same jet/rod combo, while getting a slightly richer mixture?
Gonna try to resize the accelerator pump holes and do the tip in again next week.
Cliff Ruggles:
I've set up hundreds of the large MAB carburetors with 76 or 77 jets and 44 metering rods. Never had one yet that didn't run fine everyplace. I still like going to the smaller MAB's and much smaller jetting. Dropping back to .070" MAB's and 72 or 73 jets with the 44 rods is a good place to be. The smaller MAB's richen things up clear across the load/speed range without needing huge jets. Less efficient engines will like this deal, especially those with big cams in them, relatively low compression, and poor low speed characteristics.
The accl pump is only there to cover up a potential lean condition with quick throttle movements. Might want to try disconnecting it in association with tuning the main jets, metering rods and airbleeds to take the additional fuel out of the equation.
I seldom open up the accl pump discharge holes past about .032", .026-.028" are fine for most applications. Really hard leaving cars with excellent power to weight ratios (drag strip cars) may enjoy holes up to about .036".......Cliff
Navigation
[0] Message Index
[*] Previous page
Go to full version