Steven6282

I know this question probably gets asked often, but I couldn't find anything on a quick search.

I replaced my cc quadrajet for a non cc quadrajet (doing away with my ECM completely at this point because it was giving me nothing but problems on my new engine).

I've been trying to get the carb to idle right yesterday and today and having limited success.

I've backed the mixture screws out as far as 5 1/2 turns (keeping them the same number of turns out) and can't find any setting to get the car to idle around 700-800 RPM like it should. I really want it idling in that range because I have a Lopey camshaft in my new engine and much faster than that makes the lope harder to distinguish. Besides the specs for the new engine say to set idle at 700 rpm.

I did get it idling around 750 rpm at one point today, it was at 4 3/4 turns out that it did it. But then as soon as I put the air breather back on and closed the hood it wouldn't idle again. So I guess it wasn't getting enough air or something but my air filter is not that old and still pretty clean.

A lot of times what happens is I can get it to idle around 700 to 800 while the car is running but then when I turn the car off and try to crank it again it doesn't want to idle unless I rev it to around 2k rpm for a few seconds.

Also one other question while I'm posting. I've got two vacuum lines coming off this carb, one goes to the vacuum advance on the distributor and that one is running around 13 -15 psi while idling, the other goes to the charcoal canister and is split off to a metal pipe that I think goes to the fuel tank. The second one that goes to the metal pipe has < 2 psi on it. Does this indicate a vacuum leak on that line and maybe that has something to do with my idling problems? The only reason I doubt that is a problem is because if I unplug the vacuum line and feel it with my finger, I can barely feel any suction on it from the carb so I was thinking it might just be a low vacuum plug on the carb. Which raises another question, should this line (the one going to the possible fuel line) have a high vacuum on it?

Thanks for any assistance.

el_muerte

Don't use the mixture screws to set the idle speed. There's a screw on the side of the carb where the throttle cable attaches that controls idle speed.

Steven6282

Yes, I'm aware of that. But as far as I've been told you have to set the idle mixture as well to get proper idle. If I didn't play with the idle mixture screws the car wouldn't be idling at all right now, the carb came set to 3 turns out on the idle mixture screws and at that setting will not idle without setting the idle speed screw way in idling at around 2k rpm. I didn't mention adjusting the idle speed screw as well because I thought that was a given as to how I'm adjusting the actual idle rpm.

I'm not sure if I should try going more than 5 1/2 turns out on the mixture screws or if that is obviously to far out on the mixture screws.

NCGuy68

Thoses Qjets can be a real pain sometimes and for whatever reason do any further adjustments with the air cleaner in place. I would suggest a couple very basic things at this point:

Turn both mix screws in until lightly seated. That sould kill the motor. If it doesn't, one of the screws could be bent (unlikely) or there is trash somewhere in the idle circuit. In the past, I've removed both screws and blown compressed air into each screw port. A can of PC duster should work but you may need something with more pressure. If you try this, remove the air cleaner and all vacuum lines first. Sounds crude I know, but its worked for me in the past.

You may find that the carb wants more then 5 1/2 turns out and both screws don't necessarily have to be the same. Start with both at 3 1/2 out and adj. in/out one at a time until you reach the highest vacuum reading/RPM, then do the other. Finish up with the main idle screw.

In the end, you may find that the motor just doesn't like the 700 rpm you desire and wants a higher idle. Good luck.

305eatsRice

So that is a good baseline to start out with? I'm having the same issues as Steven.

NCGuy68

Yes, 3 to 3 1/2 turns out is good. Keep in mind that this is for a know good working or freshly rebuilt carb. If it has other internal problems, all the messing with the screws in the world isn't gonna help.

el_muerte

That should be a hint... at 2k RPM, the idle circuit supplies a very small portion of the fuel used and the car will typically run regardless of your idle mixture screw positions. You could try to keep backing the screws out. As NCGuy68 suggested, checking the condition of the screws and blowing out the idle circuit might help. Also, check the carb for vacuum leaks - it could be that air is getting in somewhere else without bringing any fuel with it, which could explain why it refuses to idle at lower speeds.

Steven6282

Just an update in case anyone else has similar problems.

Turns out my vacuum advance on the distributor was connected to the wrong vacuum line. So it was advancing 30 degrees at idle and is why I couldn't get the engine to idle down below 1k rpm.

Someone else checked the timing for me today and moved it to a vacuum line that doesn't have any pressure at idle and my engine is now happily loping at 700 RPM.

NCGuy68

Yep, that'll do it everytime. Glad you got it straighten out.

Oldtin4me

get guys I have an 87 camaro with the cc quadrajet I was having issues with with it and just rebuilt it and now the choke won't turn off to let the rear barrels open I did a little rig up so they would stay open just to see how it did going down the road but it runs real poor and doesn't errant to shift right any ideas?
One more thing how do you post new threads?

ZZ3 Z28

Q 2 first, at the top of the forum where it says new thread.

Q 1, There is a lot of 411 on Q-Jets here. Try here at the tech articles section.

https://www.thirdgen.org/technical-articles

Also, I like this place,

http://forum.grumpysperformance.com/...f34c7db90a5807