I have a 1987 camaro with a qjet. The idle started getting too high so I backed the idle adjustment screw off and the cam is no longer supported by it. My idle is at 1000 rpm. where could my problem be. With the engine at 1000 rpm, dwell is set correctly, timing set at 0 degrees. I've tried adjusting the idle bleed screws in, but the idle doesn't come down.

before any one asks, the choke is full open and the fast idle cam is no longer in play.

 

Timing should be about 8-12 degrees.

Looks like you have a vacuum leak.

 

timing is set at 0 degrees with the 4 wire plug unplugged. Timing is beyond the indicator when the plug is plugged in. I will check vacuum though I guess. What should it be at at idle?

 

Mine is set at 700. With the connector pulled from the HEI, timing is set to 8-12. That's base timing. Chilton's and Haynes make poor manuals, but they do give good basic info

 

Haynes manual says "check underhood sticker for proper procedure and timing setting". The under hood sticker says 0 degrees with the 4 wire plug unplugged. Thats why I set it there. Funny thing is that when I went to double check that tonight, the idle stayed at a nice smooth 500 rpm, timing at 0 degrees, but the dwell way off. when i took the air cleaner cover off and set the dwell backk to 30* it oscillated between 28-32*. when I put the cover back on, it steadily climbed up to 45*. then I took the cover off and it came back to 30*. I took the air cleaner out and put the lid back on and it shot back up to 45* again. I checked for an obstruction and found nothing. What the heck is going on with this stupid car? It worries me even more that the problems are not constant. Where should I begin looking?
For the record, my vacuum is 18 inches of Hg steady.

 

Zero degrees base timing is the stock setting. A little advanced from there will often help the car run better, but 6 degrees BTDC is typical. More than that can get you into spark retard, which is counterproductive.

I think you were trying to say that you removed the air filter during your investigation of dwell changing.

The idle mixture screws should be set 3-3/8 turns out and left there. The idle air bleed should be used for the final dwell adjustment. You should not try to use either one to affect idle speed.

Per the factory instructions (https://www.thirdgen.org/forums/carb...e-rebuild.html), the dwell should vary between 25-35 degrees (6 cyl setting), getting as close to 30 degrees as possible. Some varying is normal. If it is going up to 45 degrees when the lid is put back on, this indicates a richening condition. Verify you aren't getting any interference with the choke mechanism (not likely, but verify it). What may be happening is the thermovac system is closing when you put the lid back on, which is more restrictive than the full-open snorkel. Try taking off the vacuum hose and capping off that port, and see if the dwell increases when you put the lid back on.

 

Yeah, I found out that the idle mixture screws will not effect idle rpm. I was turning the + or - 1/2 turn from 3 3/8 turns out, and then making final dwell adjustments with the idle air bleed. I got the dwell to sit at 30* + or - 2* with out the lid or aircleaner.
You are correct about my attempts to find the cause of dwell issues. I first saw the problem with the dwell going to 45* with air filter in the air cleaner assembly. I then took the filter out and put the air cleaner assembly back on and got the same result. I will try caping off the thermovac vacuum port and see if that fixes the problem. I already checked to make sure the air cleaner assembly isn't interferring with the choke.
Thanks for the help, I'll keep you guys updated.

 

I got everything to tune in. I got dwell set after the aircleaner was set on. The Idle mixture screws are only out 2.5 turns though. That was only way that I could get the dwell to set up right. I had to set the dwell at 20* before the air cleaner was put on. I also kicked the timing up to 4* btdc just for kicks. I haven't had time to take it out yet but it sounds really good.

 

You might have leaking well plugs. That can add fuel that isn't metered by the idle system.

That wouldn't explain the change in dwell with and without the air cleaner lid, though. It would explain why you couldn't get the dwell in spec with the idle mixture screws set to spec.

 

I've also noticed the dwell response to re-installing the factory air cleaner. Shows how restrictive the unit really is.

Have you solved your intermittent high idle issues? In the past few years I've thrown a handful of bases into the junk box for worn throttle bushings. They'll cause sticking throttle and intermittent vacuum leaks causing the dwell to hunt at idle. You can check play in the shafts after disconnecting the throttle stuff.

If the carb's never been opened a re-build may be due-replace seals/epoxy those plugs, but if it's running perfectly I'd let it be for now.

This is on a 350? I'd expect the idle mixture screws to be a little further out, but comparison to a stock LG4 is out.

 

Do you have a thermostatic air cleaner? A lot of people remove the ducting from the exhaust manifolds and that doesn't allow the door to open and it just sucks air from the little hole instead. Might want to remove the door if thats the case.

 

Check secondaries. Not unusual for the four barrel butterflies to stick open just a bit, give the high idle.

 

And check for worn throttle shaft..