I have an 81 corvette with the stock motor in it, and it has sat for a while in my driveway. I've recently been working on getting it running better. I had a friend rebuild the carb for me because he knows a lot about them. I got it all back together and installed and it's idling at about 1500 rpm. I've tried adjusting the idle screw and it didn't seem to affect it at all. I'm used to working with EFI so I'm not very experienced with carb cars. Is there another reason it would be idling so high?

 

Well I am assuming you have a Quadrajet carb..if it is..sounds like the choke linkage on the ps of the carb needs adjusted..check to see if the little arm falls automatically when you tap the throttle..if your bud rebuilt the carb he should know what that is..if it is all the way down then adjust the choke tension..ok if all this is ok check your timing..it could be advanced real high..or you have a good vacuum leak..many things need dialed in when the carb gets rebuilt..check this stuff out and see what you find!

 

He took the choke off of it because he said it wasn't working correctly.

 

And yes it's a quadrajet.

 

is there a small plunger pushing the throttle ?unplug the wire to it and see what it does .

 

Nope, everything hooked up to it is mechanical.

I don't know if this matters but I can actually push the throttle forward and it will idle down but it won't stay in that spot.

 

Ok so he removed the choke..is the linkage still there on the side? Have you turned in the idle mixture screws yet?

 

Yeah I tried adjusting the idle screw and it didn't change anything. I'm about to upload some pictures for reference.

 

how is your throttle return spring set up and do you have two springs?

 

Here are the pics:

 

whats the gap on your idle solenoid? is that plunger holding the idle high?

edit ok disregard that not all pictures opened up at first....

.try moving the springs so the pull from the top and the front and seel what that does

 

None of the plungers are holding it high I checked that. I honestly don't know what an idle solenoid is.

 

If you can push the throttle linkage forward and it idles down then you've got binding in your linkage (move the linkage assembly forward a tad) and/or the throttle return spring is weak. DO NOT take the spring off while the engine is running. Just add another additional spring as a test to see if idles down. If the easy fix as the spring doesn't do the trick, watch your throttle cable as you push the linkage forward to idle it down. See if it's over-extending as you push the linkage forward to idle it down. If so, move the throttle cable forward just a little so the throttle blades close and the throttle cable is not over-extended.
Good luck.

 

In your second photo something is holding the butterflies open. The idle speed screw is not in contact with the idle stop lever. This is the screw right below the accelerator pump lever in that pic.. Even though the choke plate has been removed the fast idle assy. is still in place. There is a fast idle screw on the pass. side that rides up on a lever as was posted earlier that is most likely what is holding it open. First pic. shows slow idle adj. screw. Second shows a typical fast idle adj. screw on the pass. side of carb. mike...

 

on the fourth picture down you can see the idle solenoid as the cylindrical piece with the black wire and white clip fastened to it. There is a HUGE gap between the plunger and the edge of the throttle assembly.

 

I would try all the previous poster's suggestions first. It doesn't look like the idle screw is contacting the carb linkage. If the throttle plates were taken off the shaft it is possible to put them in wrong and your binding may be there. When the butterflies close they are really tight in the throttle plate. There is a cross hatch pattern on the throttle plates on one side, make sure they are oriented the same by looking down the venturis. I am almost sure that the cross hatching should not be visible through the venturis it should be visible when you take the carb off and turn it over. I haven't fooled with a Q-Jet in a while but I seem to remember having this problem myself.

Also, 1981 was the only year carb to have electronic controls on it and then they went to F.I in 1982 ( on Corvettes that is). Have you hooked up the electronics to this carb? I see in your pics that none of them are hooked up.The Blue connector is for a float height sensor and I can't remember what the 4 pin white connector does (someone out here does). If you aren't planning on using those electronic controls and you don't care about originality, pitch that thing and replace it with a Holley 650 if it is a standard or get a 1973-80 Q-Jet if its an automatic. My 2 cents. Good luck!

 

Your throttle blades are partially open. You can clearly see it in the pictures.

You need to adjust the fast idle cam as noted above.

 

First off, if your friend knows Q-jets, he should have left the choke plate in place and fixed it. The fast idle works of the choke linkage. The selonoid that's on the carb is for the AC. When the AC is on, it energizes and kicks the idle up a bit. Is there a reason the MC selonoid isn't connected in the pics? How about the TPS, it's not connected either. You have an electronic Q-jet and for it to work properly, it has to be connected correctly, or gutted and modified. Based on what I'm reading and seeing, I'd bet the Idle Air Valve isn't adjusted even close to correctly, and the rich/lean stops for the MC selonoid is likey AFU too...