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-   -   Quadrajet Idle Problems (http://www.hotrodders.com/forum/quadrajet-idle-problems-207455.html)

69chevyLWB 10-21-2011 09:25 PM

Quadrajet Idle Problems
 
I recently rebuilt my quadrajet and tested it out on a bone stock 305. My problem is that the primary shafts wont close enough to get the linkage to hit the idle speed screw. so it idles at around 1000 and wont come down unless you pull on the linkage. I dont know either exactly where i should have my mixture screws turned to. it seems like they dont make much happen when you turn them. Any questions feel free to ask.
Thanks, Logan

cobalt327 10-21-2011 09:35 PM

Most likely the fast idle cam is contacting the fast idle screw and hanging the primary throttle blades open. Examine the choke area very closely and you will likely see the problem.

With the choke wide open the fast idle cam should allow the blades to fully close when you open the throttle some, then allow it to close again. When the fast idle is disengaged, the curb idle screw will contact the linkage as it should. Once that's taken care of, the idle mixture screws will become responsive.

V8&4spd 10-21-2011 09:40 PM

It does sound like the fast idle cam. Once it's running kick the gas pedal. It should kick off the fast idle cam and the RPMs should go down.

69chevyLWB 10-21-2011 09:45 PM

I went out and looked at it and adjusted the screw both ways with no luck. even when the choke is completely off the linkage wont contact the screw.

V8&4spd 10-21-2011 10:02 PM

1 Attachment(s)
The fast idle cam has steps on it. If it's not adjusted right it can prevent the throttle plates from closing.

69chevyLWB 10-21-2011 10:26 PM

Okay i looked it all over again. and this is what i found: the primaries are closed fully but it still will not idle down past 1000. the fast idle cam is freee and not preventing movement so it is not that.

cobalt327 10-22-2011 04:38 AM

A couple things to try...
 
Quote:

Originally Posted by 69chevyLWB
Okay i looked it all over again. and this is what i found: the primaries are closed fully but it still will not idle down past 1000. the fast idle cam is freee and not preventing movement so it is not that.

If the primary throttle blades are all the way closed and the idle is still too high, the idle screw can be moved back out once the problem is found, so that you have idle speed control. If it's not touching now, it's only because something else is causing the idle speed to be too high.

A vacuum leak can cause a too-high idle. Try removing the vacuum lines one at a time and plugging the port at the carb and see if you find one that will drop the idle speed down when it's removed and the port in the carb plugged. There are also vacuum ports on most intake manifolds- do the same to them.

Did this particular carb EVER work right? If it did, the gaskets that were used at rebuild may have been the wrong ones, or if you don't know what the carb was like before being rebuilt, it may have already had the wrong gaskets in it and if you replaced them exactly, you recreated the original problem.

Look to see that the secondary throttle blades are not hanging open. Some Q-jets have a link that locks the secondaries from opening when the choke is closed. If yours has this link be sure it will work to keep the secondaries closed- this will show you the secondary throttle shaft is fully closed. Be sure the sec. shaft isn't twisted, allowing one blade to be open while the other is closed.

TommyK 10-22-2011 06:23 AM

Worn throttle shaft bushings can also be a source of unwanted idle air. A warped base plate can do it to.

69chevyLWB 10-22-2011 11:35 AM

All the gaskets were ordered from Cliff Ruggles by carb number. I will have to try the vacuum hose plugging and such. My dad thought it may be a bad shaft too so we sprayed carb cleaner and ether and even wd40 around them and got not change in idle speed so we dont think that could be it. The secondaries are 100% closed and i do have the secondary stop on and it is working.

69chevyLWB 10-22-2011 12:55 PM

UPDATE: It now idles fine. it was the fast idle cam you guys were right i just had to get my finger under there to release it. now when i took it for a test drive. if i give it any amount of gas it bogs out and almost dies. should i adjust my APT screw? the reason i have this on my 305 is just to test it out to make sure everything works. it will eventually be going on a built 355 sbc making around 400 hp. it has 71 jets in it right now. any help is aprecciated.

TommyK 10-22-2011 02:39 PM

The first step in diagnosing a carb problem is making sure your ignition system is properly set up and functioning. What is your initial timing?

In your original post you stated you were unsure how to set the idle mixture screws. Do you have a vacuum gauge? If so after you have the ignition sorted start with the idle mixture screws two full turns out and then with the vacuum gauge hooked up adjust the screws out in quarter turn increments until you have achieved the highest vacuum reading. If the vacuum reading goes down or is unchanged try adjusting the screws in using the same procedure to find highest vacuum reading.

cobalt327 10-22-2011 08:51 PM

Quote:

Originally Posted by 69chevyLWB
UPDATE: It now idles fine. it was the fast idle cam you guys were right i just had to get my finger under there to release it. now when i took it for a test drive. if i give it any amount of gas it bogs out and almost dies. should i adjust my APT screw? the reason i have this on my 305 is just to test it out to make sure everything works. it will eventually be going on a built 355 sbc making around 400 hp. it has 71 jets in it right now. any help is aprecciated.

You can do Ruggles' "tip in" method for setting the APT. If you set it right for the 305 you'll need to reset it for the built 350, most likely.

Also, with the engine off check the accelerator pump shot top be sure you get two strong streams from the shooters as soon as the throttle is opened.

Be sure the choke isn't closing on you.

Be sure the secondary air valve isn't set too loose or it'll open too early and will bog.

Check the timing to see that you have enough initial. Even a stock 305 can stand 12. Hook the vacuum advance to manifold vacuum if it's not already. You'll have to lower the idle speed using the curb idle screw. Readjust the idle mixture screws and road test it safely.

69chevyLWB 10-22-2011 09:19 PM

I will have to try out the tip in method, forgot about that.
The secondaries have about 3/4 turn on them. There is two good streams coming out of the accelerator pump. i started it up again and it kind of surges and as a rough idle. i dont really know what to do. getting frustrated. on monday im gonna call Cliff and see what he thinks. not that you guys arent good help its just i bought the parts from him so maybe he'll have a better idea.

cobalt327 10-22-2011 09:29 PM

Quote:

Originally Posted by 69chevyLWB
I will have to try out the tip in method, forgot about that.
The secondaries have about 3/4 turn on them. There is two good streams coming out of the accelerator pump. i started it up again and it kind of surges and as a rough idle. i dont really know what to do. getting frustrated. on monday im gonna call Cliff and see what he thinks. not that you guys arent good help its just i bought the parts from him so maybe he'll have a better idea.

Double check the easy things first- the firing order (1-8-4-3-6-5-7-2) and be real sure #5 and #7 isn't swapped at the cap or at the plugs. The plugs should be fresh. Cap and rotor good, wires good. PCV connected and plumbed right.

Check closely for vacuum leaks and be sure of the timing. These are all things Cliff will no doubt also want you to double check, so that way you can eliminate them before calling.

Good luck.

69chevyLWB 10-22-2011 10:26 PM

Cobalt327
thanks for all the help!
it has a brand new distributor in it and the engine as been running before and i didnt change anything besides the carb. pcv is plumbed all plugs checked and distributor working fine. i think that is somthing i did wrong when i rebuilt it. it idles fine sometimes then others wont idle for crap. i have never been able to give it any amount of gas when i am driving or it just falls on its face. you can revv it to the moon when its just sitting in park but with any kind of load it just nosedives.


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