Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Idle problem

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dlphil10:
Light throttle seems to be good. Plus, when the car is warm and in park, the idle screws turned all the way in don't stall the motor. They definitely choke it down though. So I don't think the idle circuit needs any more fuel correct?

Cliff Ruggles:
Correct, if you can slow the engine you have control of the idle fuel.  There is usually enough transfer slot exposed so that fully seating the mixture screws may not kill the engine clear out.  That fact varies from one Q-jet to another due to how much bypass air is used, how the idle system is set up, and the length and location of the transfer slots.  If you take a look at a few dozen baseplates from different Q-jets you'll quickly notice that the specific location and length of the transfer slots can vary considerable from one to another. 

This is why I always recommend to be very careful and conservative with idle system modifications when setting up your Q-jet for a non-stock application.  I would also avoid swapping parts around from one unit to another for the same reason.  The parts may look the same but there are minor differences in them you may hot see that will effect the end result, sometimes negatively.........Cliff

dlphil10:
Well that is good news. This baseplate looks like it matches woth the bowl. No passages are blocked and the transfer slots are long. There's even one horizontal slot as well. Maybe I could drill out the idle air bypass a bit and regain more of my transition slots? I believe they are only 0.040" right now. This may help with my part throttle response too correct?

Cliff Ruggles:
If you aren't seeing fuel coming from the nozzles at idle (nozzle drip) then it will have enough idle bypass air.  This assumes that you also have control of the idle fuel from rich to lean with the mixture screws.......Cliff

dlphil10:
I switched to the green power piston spring and that seemed to help power at part throttle. It also really seems to transition through the pedal amd the other carb circuits pretty nicely. No bog when the secondaries open. Really the only thing is a slight hesitation sometimes off idle amd a minor flat spot off idle. Power piston gives healthy squirts on the outer hole of the lever. I'm thinking I may need a bit more timing off idle honestly.

The only thing that makes me concerned is the tiny black speckles on the porcelin. They aren't heavy or shiny, amd there isn't a lot of them. Plugs are white after idling still, but 1.5 turns out is where the vacuum stops increasing. I ran them out to 6 to see if I could get the plugs to change, but they didnt. It seems to have the fuel it wants so I don't know if the specks have been on the plugs when I got them or what.

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