Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Lean Idle solutions?

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carmantx:
What size are your idle tubes and down channel restrictions?  That is a 79 403 Quadrajet.  Probably lean on idle circuits and small holes under air idle screws.

Cliff Ruggles:
76 jets are HUGE in one of those units. 

For certain increase the idle tube size and open up the idle down channel restrictions to give the engine more idle fuel.

We don't sell a "silver" PP spring, so can't advise there. 

The 79 carb will have fine pitch metric threads for the idle mixture screws, so not uncommon to have to back them out 4-5 turns or so to start finding the idle fuel you need, compared to 2-3.5 turns out for the earlier units with 10-32 threaded screws......Cliff

77cruiser:
Gotta ask about your timing though. Looks like you need to add about 20 degrees.

pauls428:
they say most carb problems are timing problems, like I said at idle 3* timing not using vacuum advance if I remember correctly (and don't hate me for this) but the cam was installed a degree and a half retarded. ill have to borrow the timing light from work and find a spec to work from..... as far as idle tube restrictions I am not really set up or all that comfortable to modify that, I will measure them and get back about it.... as much as a pita this has been it has been interesting learning how the circuits overlap and can compensate for one another.... how the car runs differently. on the other hand, maybe just another q jet is in order.

RLF:
I could never get mine to idle any richer than 14.5:1 on the AFR meter but I noticed the exhaust was getting blacker as I richened up the idle circuit. For whatever reason (maybe large cam) it always reads lean at idle even though its rich.
If it idles strong I wouldn't be too concerned, same with your lean cruise as long as the AFR's richen up with power piston movement.
You do have ignition timing to sort out though!

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