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Q-Jet Rich transition from idle to off idle

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79Firebird_99TA:
This q-jet was rebuilt and modified by Cliff 10 plus years ago. It was due for a rebuild as it had some junk in the float bowl. After getting it all back together it has a rich condition when flicking the throttle off idle. I've adjusted the APT, fuel mixture, secondary flap spring ... so all that is good. When I take off the accelerator pump rod, the throttle response is really good.

I think that the power piston spring was a bit too stout so I'm going to put in a lighter spring. Does this sound like the issue and/or jet/rod combo? I don't know what the jets/rods are.  I'm only doing around 12hg of vacuum and I tried manifold and ported vacuum to the advance can. I prefer ported which is where I've left it. Any assistance is appreciated.

Cliff Ruggles:
What is the carburetor part number?

Engine specifications?

What did you do to the carburetor aside from installing new internals?

79Firebird_99TA:
The carb is a 17057262. The engine is a 400 with an XE-268 cam/4 speed/3.08 rear. I've got 6x-4 heads on it; they're milled .065". I think that puts it at 9.2:1 SC. I use ported vacuum ... at idle I've got 12in. hg. As far as the internals, I only cleaned the carb and replaced the internals with your kit. The idle mixture screws are right at 4 turns out and the APT has it's highest RPM (starting 1500 rpm at 4.5 turns out. ) Throttle response is fine when cold. 

79Firebird_99TA:
I put a lighter power piston spring in it (the orange in the 1994 edelbrock kit).  It's supposed to be for 12 in. hg of vacuum at idle which is what I have. Didn't help one bit. I'm actually going to put the previous spring back in it. I have a fairly tall accelerator pump duration spring in it. Should I go shorter? There was a shorter spring that came with the kit which I didn't use.

Cliff Ruggles:
I'm slightly confused.  Are you mixing parts from one of those Edelbrock tuning kits for a 1910 into the deal here?....

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