General Category > Quadrajet Carb Talk and Tips
86 c20 4 bbl carb (failing smog high nox new cat)
Cfrench192:
It's a 20$ retest. I have a new egr valve so I will be replacing it before hand.
Cfrench192:
Ok so here's the results still failing.
15mph
Hc: 19 max 122 Co 0.00 max 1.96 Nox: 2769 max is 1591
25mph
Hc : 13 max is 77 co is o.oo. NoX is still very high at 2322. Max is 1537
The cruise did richen after the apt adjust. It had little to no effect for noX.
I guess I should play with the timing. I tested the egr and it still works. It can hold 15 inches of vacume with no bleed off. If I open the egr with a pump, it will stall the motor.
I'm going to aim for dropping the timing to 8 btdc and switching the vacume advance to ported instead of full manifold.
Does anyone have any other ideas on this.
DieselPower:
How is your EGR valve controlled? The valve itself may be fine, but the control side has a problem.
Cfrench192:
The egr is controlled from ported vacume. No electronics. The truck has no computer and no sensors. I readjusted the timing.
The motor is at 10 degrees initial. The distributor is all in at 2800 rpm (27 degrees)+ 10 initial= 32 total. When I bring in the timing with the vacuum advance I get 50 degrees.
It picked up some performance but I have a low end pinging and high end. The a/f guage is still lean (17.3).
Due to this I think the rod/ jets are wrong. Does anyone think I should jet bigger with a rod with a smaller metering area? It's obviously not getting enough fuel.
Cliff Ruggles:
The factory used a special ported vacuum slot for EGR, with a bleed-off port so it doesn't fully open the EGR valve at light load/light throttle cruising. Make sure your carb has the correct port, it as in the baseplate, passengers side on most models.
The correct ported distributor port is on the drivers side, front of the main casting to the right of the fuel filter housing area.
Since you are dealing with a "remanufactured" carburetor and not a rebuilt original unit, many items inside the carb may be altered, or not factory sizes. They also miss-match components, so it's not surprising the carb is out of spec.....Cliff
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