QJet Question...again! - Team Camaro Tech
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post #1 of 3 (permalink) Old Aug 18th, 03, 06:01 AM Thread Starter
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Join Date: Sep 2001
Location: Queen Creek AZ
Posts: 3,677

I rebuilt a QJet and have been messing with the mixtures using my narrow band O2 sensor. I have some questions....

At idle I can adjust the idle screws to get it to stay in the .30 - .50 range. The engine runs OK idling in park, but while driving with accessories it runs kind of crappy set that lean. Using the old school method using a vacuum gauge/tach it seems to idle best on the rich side. Does that sound right?

I have a holley 110 GPH fuel pump and a pressure regulator. I have the pressure set to 6 PSI, anything higher than that tend to overrun the needle/seat. Is 6 PSI still too high?

From a stop on a flat road, at idle it's running on the rich side. I gently press the pedal(to avoid the accelerator pump shot) and the mixture goes lean and stays lean(no surging though, engine seems to be running fine) until I hit cruise speed and back the pedal off. While staying at a constant speed on a flat road the mixture again goes rich. I have tried different rods/jets and it always seems to go rich at cruise. I'm wondering if it could be pulling fuel in from somewhere at cruise when the vacuum is high. I set the float a 5/16 and when I pull the carb off the fuel level looks fine.

I just can't see anyway that the cruise mixture could go rich unless fuel is coming in from somewhere else. If the metering area was too big i t would be rich, but I have tried very small combos like 67 jets/46 rods with the same result.

I have no experience with QJets when they were in original like new working condition, so I have no baseline to compare to. I have only rebuilt the old "sat in the parts pile for years" type carbs, so it is feasable that the cores that I have been rebuilding could have problems.

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post #2 of 3 (permalink) Old Aug 20th, 03, 06:14 PM
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Join Date: Jan 2001
Location: Raleigh, NC
Posts: 1,046

Don't overlook the choke ... I bet it is out of adjustment and not working properly ...
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post #3 of 3 (permalink) Old Aug 20th, 03, 07:33 PM
David Pozzi
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Join Date: Nov 1999
Location: Central California, USA
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There is an adjustable stop for the metering rods. Early carbs had a screw coming in from the front, later carbs had an aluminum plug right over the adjuster. You can pop the plug out and tap it for a small pipe plug with allen head, remove the plug and turn the screw.
You would have to make a device to turn the screw with out of tubing squashed a bit to fit the screw.

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