Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

Rebuilt Rochester E4ME on a 1981 Corvette Code 45 Running Rich on Highway

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Reaper19:
Carburetor dialed in finally. I could not get the idle running right or dwell dialed in unless the IAB was only 1 turn out. I took the IAB all the way out and found when this carburetor was built the bottom o-ring must have fell off and was at the bottom of the opening. Being the weekend I found a replacement at the hardware store, installed and now I am able to set everything, dwell at 30 degrees, idle mixture screws 3 1/3 turns out, TPS at .56, timing 12 BTDC and idle 600 in drive. Factory idle is 500 but with the new cam it likes 600 better.

The problem I now have is a rough or off idle and the motor shakes a little, not a smooth idle. Any ideas?

Cliff Ruggles:
I have the correct "O" rings for the valve in stock, and would put the correct ones on it.

The upper IAB adjustment allows the tuner to have full control of fuel at idle speed, when the carb is set up correctly.

If there is a vacuum leak someplace, or throttle plates not indexed/sealed up, or a leak at the primary shaft, getting a smooth idle may not be possible......Cliff

Reaper19:
Thanks Cliff, I ended up taking the carb back to the rebuilder. The TPS was bad and replaced, new O-rings installed and lubed. I am able to get the dwell set up correctly but it still has a little off stumble/rough/surge at idle, otherwise the
engine is performing better than ever. I am able to smooth it out by changing the factory suggested idle from 500 to ~650 or more while in drive. I did have a little bigger cam and higher compression pistons installed when the engine was rebuilt, might be the reason it wants more idle RPM. Also, I have timing set at 12 BTDC. I checked all vacuum lines found that the cruise transducer was leaking so I plugged that line for now. I capped all vacuum ports one at a time and no change, except when I remove the map sensor vacuum line, the car really runs rough if unplugged.   

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