rebuilt quadrajet

[thump16]

how accurate are the settings on rebuilt quadra jets. the one I installed is a headache. Stalls at lights and wants to mist at idle.

[Malo83]

Where did you get the Qjet?
I got my rebuilt Qjet from Carbs Direct and she's been running great since it was installed 4yrs ago, only thing had to adjust was air screws and idle speed screw.

www.carburetorsdirect.com

[thump16]

got it from advance. It acts like it isn't getting any air until you either stomp the gas or advance the timing. Should I adjust the front screws? It drinks gas aslo.

[Kixwy2]

On mine, which is a Rochester, there are two sets of screws - one for mixture that is gold, and the other set is slow/fast idle (silver, smaller screws set back on front). When the shop that rebuilt mine gave it back to me, they said I would probably have to fiddle a bit with the idle and mixture depending on the truck components, and the way it was timed. Sounds like your fast idle is ok but your slow idle is too low. If your timing is good, turn your driver side silver screw in or out a half turn and see if that helps you at stops/lights.

I'm not an expert by any means, but the guy who rebuilt mine is... he gave me some great tips.

Edited to add: if you are guzzling fuel, your mixture is not appropriate. Factory spec on the Rochester is 3 full clockwise turns on either side... I think Holley might be 2.5? Turning clockwise on a Rochester will lean the mixture so you don't use as much fuel.

[James McClure]

Thump: morning. How did truck run BEFORE carb change? Is EGR closed? Are all the vacuum lines good and attached to the correct ports? Is the power brake booster leaking internally? Most rebuilders set the carbs pretty close to what they are supposed to be. If carb "fogs" after shut down with a warm engine, float level is to high. With engine idleing use a rag or the choke butterfly to choke the engine a little at a time and see if engine smoothes out. If it does it's lean. At the very bottom of the carb there are 2 screws. These are your idle mixture screws. With special tool, back each one out in 1/4 turn incriments. If it's an 84 it isn't a feedback carb (computer controlled carb). Thats about the only adjustment you can make yourself except for idle speed. Metering rods can be adjusted but thats something that you shouldn't tangle with unless you rebuild QJ carbs. If you find everything external to the carb to be OK, take the carb back to the vendor. Mine is an 84 k20 with a 350m engine and 465,000 miles on it. I've rebuilt the carb 4 times since I got it. I know how to from dealer expirence, so to me it's easy, but to you I can imagine it's daunting. I'm doing a complete restoration on mine now. It's the last vehicle I'll own so I want it to last. I'll be dead before that truck is. Throw my coffin in the back and cart me to the cemetery. Hope this answers some of your questions. Jim Adjusting Idle mixture screws will not help with fuel consumption issue. Once the throttle plates open they are above the idle ports and fuel ceases to flow out them. Fuel over consumption is caused by to high a float level OR metering rods set incorrectly or broken. What I am saying here is only where the carb itself is concerned. External problems will affect mileage but I'm not refering to them, only the carb. Jim

[thump16]

I noticed that if you manually adjust the choke plate towards closing the engine smooths out nicely so maybe it is fuel. All the lines are hooked up and the egr seems to be working perfectly but it stumbles like crap when giving it gas. It is a rochester.

[thump16]

Thanks for the ideas so far guys.

[87Bob]

Originally Posted by thump16

how accurate are the settings on rebuilt quadra jets. the one I installed is a headache. Stalls at lights and wants to mist at idle.

I just had mine done here in Indy and the guys that did it tune on an engine in their shop. I got it home and bolted it on started it right up it drove fine I just had to slow the idle down a little. It was done by Vans Auto Eletric. It looks as good as it runs.

[60-66 Nut]

Thump, I would be sure to check the EGR valve as Jim mentioned. If it's not closing properly, it amounts to a giant vacuum leak. It can also cause a very bad stumble on takeoff. Just tap on it with a hammer while the truck is idling and see if the engine trys to straiten up. In case you're not sure where it's at, just look at the picture Malo83 posted, it's the brass colored diaphram bolted to the intake on the side of the carb with one vac hose on it. Hope that helps, best of luck.

60-66 Nut

[Thumpin455]

OK first things first. James has some very good info, take his advice. Quite often a Qjet "rebuilder" wont have them set up correctly, and often the only ways to fix the problems are start over with a new carb (particularly when they have messed up threads or done other bad things in the 'rebuilding' process) or take it completely apart and put it together right.

If you want to know more, or rebuild your own carbs, get this book. It has detailed info and Cliff is the Qjet Guru.
http://www.amazon.com/Rebuild-Modify...8011578&sr=1-1
I dont care where you get it, just showing an example and what to look for.
The screws under the front dont affect anything other than idle mix, after the engine is above idle they do nothing. They dont adjust the fuel flow for the primary or part throttle, that is handled by jets and metering rods.

If you are having a stumble off idle, it could be a number of things, but the first to check is the accelerator pump, push down on it and see if gas shoots in the carb. If that is good then its on to other things.

Float level makes a huge difference in how a carb runs, if it is too low, it will stumble and run lean, if its too high, it will run rich. Both rich and lean will cause that burning your eyes sensation. The only way to adjust it on a Qjet is to pull the top cover, if you havent done it before and know nothing about carbs, dont do it.

I never run the stock type fuel filter, its right behind where the line connects up front. I use an inline filter ahead of the carb/pump. The cheap filters can severely restrict fuel flow and a clogged one is even worse. Definitely run a filter, Qjets dont like junk inside them.

If its bogging from part throttle, then its the secondary air flap opening too fast, there is an adjustment screw for that, with an allen head screw that locks it in.

There is plenty more info to give, but its difficult to give the best advice without knowing exactly what its doing. They are great carbs, most people just dont know much about them. They are capable of serious power and economy with the same settings, but if the rebuilder doesnt have a clue, it will run like junk.

Best advice I can give you is spend the $16 and get Cliffs book. I dont get anything from him when he sells them, I just build Qjets..

[thump16]

Okay so I adjusted the screw out one and a half turns on the carburetor drivers side and the truck picked up life. Does that add fuel or air? It still stumbles a little but I hope I am on the right track. Should I have adjusted the one on the passenger side also.

[87Bob]

Originally Posted by thump16

Okay so I adjusted the screw out one and a half turns on the carburetor drivers side and the truck picked up life. Does that add fuel or air? It still stumbles a little but I hope I am on the right track. Should I have adjusted the one on the passenger side also.

In a word yes. You need a hand held tach the're fairly cheap. Start by turning one mixture screw in untill it starts to stumble. Then back the screw out untill you gain no more RPM then 1/4 of a turn more. Do this on both sides. I do it twice just to be sure. If its an automatic get a friend to sit with the BRAKES APPLIED (make sure there is nothing behind the truck) and in Reverse set the idle to about 700 RPM with the air con off. That should do it. The only other adjustment is the choke for that you need to check the manual.

[thump16]

I noticed this morning that it drove a little better but it still stumbled when giving it slight gas. I will go back and turn the other screw today and possibly start over. I never messed with them because I thought it would be simple plug and play. Also i noticed it would sit some times and then load up and shut off.

[87Bob]

Originally Posted by thump16

I noticed this morning that it drove a little better but it still stumbled when giving it slight gas. I will go back and turn the other screw today and possibly start over. I never messed with them because I thought it would be simple plug and play. Also i noticed it would sit some times and then load up and shut off.

The loading up and stalling out sounds like it might be float level related!

[thump16]

how do you adjust the floats?

[87Bob]

Originally Posted by thump16

how do you adjust the floats?

For that you should probably have a manual, sometimes the library has them. Try setting the other items first. Then if you have a problem check the floats.

[James McClure]

Sledge: You don't adjust the float, not unless your VERY familiar with the workings of a QJ. Just take it back and start over with idle mixture adjustments and idle speed. In answer to your question from above post, the idle mix screws control fuel not air. Adjust BOTH screws the same way at the SAME time. Screw idle mix screw in till engine starts to stumble, back it out until you get the smoothest idle you can, then do the other side the same way. Go back and do it again to be sure. After you have done the adjustment to each idle screw twice, back them both out 1/4 turn. Make SURE to alternate left to right or right to left during this procedure to be sure your getting the best results you can get. Like this. adjust left, adjust right, then go back and adjust left and then right. Jim

[alextreme76]

my truck has a similar issue, it is supposedly a new carb, but it is clearly rebuilt at best

the secondaries never open, but it never cuts out at higher rpm or when i stomp on it at higher speeds...?