Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
7041540 Buick 455 goes lean at WOT
Rhett:
Yeah I checked that, it actually wasnt the idle that was a problem (although It could have used more bypass), it was the cruise/primary power/WOT circuits that just were overwhemed. On both the 540's, the .152/M4M float combo seems to work well at .250, the airhorn gasket just weeps a little.
Kenth:
Unnecessarily high fuel pressure, an unnecessarily large needle valve and an unnecessarily high adjusted float will invariably work together to cause an excessive fuel level in the float housing resulting in all circuits delivering fuel too early and causing the problems you describe.
70GS455:
--- Quote from: Rhett on August 26, 2024, 05:07:07 AM ---Yeah I checked that, it actually wasnt the idle that was a problem (although It could have used more bypass), it was the cruise/primary power/WOT circuits that just were overwhemed. On both the 540's, the .152/M4M float combo seems to work well at .250, the airhorn gasket just weeps a little.
--- End quote ---
You are having the same problem I was. The issue is the secondary well tube restriction (secondary high speed air bleed) is too big. I reduced mine to 0.025" and got the AFR curve to be much flatter. Plus my air door is way open (1.240").
Read the graphic in this post. https://www.tapatalk.com/groups/racingfuelsystems/viewtopic.php?p=16572#p16572
Rhett:
--- Quote from: 70GS455 on November 06, 2025, 06:53:45 AM ---You are having the same problem I was. The issue is the secondary well tube restriction (secondary high speed air bleed) is too big. I reduced mine to 0.025" and got the AFR curve to be much flatter. Plus my air door is way open (1.240").
Read the graphic in this post. https://www.tapatalk.com/groups/racingfuelsystems/viewtopic.php?p=16572#p16572
--- End quote ---
Thanks Scott, mine are opened up to .037. At the time that made sense to me but looking back, the origionals (.026 I believe) were sized to work with a whole assortment of OEM rods, right down to .0300.and my RPM's are within the OEM service range too. I had always considered the secondary AF's be linear, had not considered the exponential air intake of RPM (as shown in the graph) against the fixed fuel metering. I've got a spare set of tubes and I'll give your suggestion a try.
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