General Category > Quadrajet Carb Talk and Tips
M4mE California emmissions Chevy 350 Chevy c20
Jeffs68:
Ok, the bag of marbles situation sounds like your pinging under load due to ignition timing or a lean condition which explains the HI Nox numbers.
What is the factory timing spec? 0 degrees?
Do you have oversize wheels and tires on that rig? I've seen them cause Nox failures before...too much load on the engine.
I would put a vacuum gauge in line with the EGR vacuum line and stick it on your windshield and see if you are actually getting enough to pull the valve open.
Cliff should be able to tell you if your carburetor is too lean, that also would explain the HI Nox.
What year is the truck/engine?
Those emissions readings are actually quite good, with the Nox exception.
Cfrench192:
Ok so the truck is a little bit lifted with larger than stock tired. It has a th350 transmission with 4.10 gears in the axle. The truck is a 1986 c20 3/4 ton. The motor was out of a 93 suburban. It is a 5.7. I had to put in an electric fuel pump because there was no mechanical provision in the block. The factory spec for this year of truck is 6 degrees. I'm at like 2-4 to prevent misfiring. Total I only get like 20- 22 w/ vacuum advance. From what I have read. These carbs were set up lean for emissions purposes. This is what I believe my problem is.
Jeffs68:
Definitely sounds like the motor is looking for more fuel.
Hopefully Cliff will chime in with a calibration recommendation for the carb. Also, post the carb number so he knows what you're running.
Cfrench192:
17085000 is the carb number. You may be correct about insufficient vacume to egr. At these rpms the egr only gets a couple of inches of vacuum. I have a theory that if I open up some restrictions for the idle circuit, more hydrocarbons in the combustion chamber will help cool the motor down a little bit. As far as coolant temperature my Guage only reaches about 120. I have a really big radiator I'm this thing.
Jeffs68:
I'd wait to see what Cliff says about that carb, and then I'd focus on the EGR vacuum source issue. Does it come from a ported vacuum switch or an EGR solenoid vacuum switch.
Either way, I don't think that valve is lifting enough to allow enough exhaust gas into the combustion chamber.
What T-stat temp are you running?
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