Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

quadrajet 7042210 idle question

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gclark:
Cliff,

I currently have the mixture screws set about 3 turns out.  This is where I get the highest vacuum reading (about 14").  I can kill the engine by turning either one or both screws all the way in. 

Thanks for the help.

Cliff Ruggles:
Geoff, if you have full control of the idle fuel, and no "nozzle drip", engine speed doesn't fall off a lot when you place the trans in gear, etc, that may be about as good as it gets with your particular combination of parts.

I really LOVE the rumpity/rumpity sound from aftermarket camshafts ground on tight LSA's, but they comprimise idle quality in many cases.  You can take the same basic cam and grind it on a 112 or even a 114LSA and the engine will idle much smoother, with a broader/flatter power curve. 

However, not nearly as much "bling" as the "performance" oriented grind........Cliff

73ss:
My combo stunk quite bad as well from the exhaust. The engine seemed like it had enough idle fuel. I pulled the tubes and replaced them with new ones opened up to .038". Stock measured .035". I got more control of the mixture screws & the exhaust does not stink nearly as bad although it does still smell. Also picked up about an inch of vacuum. Cam is 110 degree centerline. My 2 cents.

gclark:
All- Thanks for the replies.

Cliff-  My idle speed is 800 rpm in park, 600 rpm in drive. 

I don't know about the nozzle drip- how can I determine if I have this?

Also-  if I pull the cap off of the vacuum port on the side of the carburetor at idle speed(800 rpm), the engine speed increases by about 75 rpm.  Does this mean anything at all?

Thanks for the help.

Cliff Ruggles:
When you add more air, the idle speed is going to increase a tad.  If the mixture is slightly rich it will also increase and smooth out some.  If you are right on the edge of being lean, it usually invokes a slight miss into the exhaust note.

To look for nozzle drip, glance into the carb at idle speed and see if any fuel is flowing from the boosters.  If not, the carb has sufficient idle bypass air and the plates are closed enough to keep you on the idle curcuit.

200 rpm is a pretty big drop when placed in gear, is the timing rock stead when this is happening?.....Cliff

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