Cliff's Quadrajet Parts and Rebuild Kits
Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: alrobjr on March 29, 2012, 04:13:30 PM
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Can you tell me the correct way to adjust my fuel mixing screws on this 4-barrel q-jet , my car has a strong gas odor when idling and the plugs will have soot on them. This is a Buick 350 engine with a thumpr 279 cam and the rest is stock .
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Good luck. The Thumpr cam line is specifically aimed at folks who don't care about power, as long as the idle is crappy.
Connect a vacuum gauge to manifold vacuum. Adjust idle mixture screws to achieve highest vacuum. Reduce idle speed to correct RPM, and adjust idle mixture again. Repeat as needed.
Once you have highest vacuum at proper idle RPM, turn screws about 1/8 turn IN (lean). Just enough to reduce vacuum by about 1/2 inch. Slight lean drop dramatically reduces tailpipe emissions without much compromise in idle quality.
Keep in mind that "strong gas odor" when idling is likely due to NOT ENOUGH idle fuel, the mixture is so lean that it misfires. This is made worse by the camshaft overlap.
Stock engine? I'd rip that Thumpr out in favor of a cam that worked.
http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1453&sb=2
Comp claims: Choppy/thumping idle. best with 2000+ converter
They're showing 77 degrees of overlap (advertised--.006 lift)