QJet Adjustments

[Mattman2010]

I have a 1980 K10 with a 350 in it with a Qjet. I am having problems with to much fuel being dumped into the engine when I stomp on it, or at wide open throttle. When stopped and the throttle is pushed to the floor, the engine bogs down a lot, and there is the smell of gas that gets into the cab. But if the throttle is slowly pushed it runs fine. At higher speeds when the throttle is pushed to the floor it will run fine till its RPM start to get high (About 2500 -3000) and starts to bog down unless you let off the peddle a little then it starts to get the power back. But I am pretty sure that there is to much fuel being inject at these times because of the smell of gas that gets into the cab. What do I need to adjust the Qjet, and how do you go about adjusting it to run the best?

Also, what is probably the highest RPM you want to push a stock 350? I am doing about 3000 RPM doing 65 - 70 MPH, is this high, or is it fine?

[garmar]

My 84 with a 305 and Q-Jet does the exact same thing. I'll be watching this thread.

[irishman999]

Try adjusting that bad boy, when you stomp on the gas it pushes that rod down and squirts it in your carb. There is two holes the rod could go in, You can also bend the end of the stamped metal rod according to the how to guides I have read.

[irishman999]

My first question is, Do you see alot of black smoke when you mash on it? The Quadrajet is vacuum operated so it should not be dumping gasoline unless you have enough vacuum to open the secondaries. Is your carb the original one on your truck?

[Mattman2010]

Originally Posted by irishman999

Try adjusting that bad boy, when you stomp on the gas it pushes that rod down and squirts it in your carb. There is two holes the rod could go in, You can also bend the end of the stamped metal rod according to the how to guides I have read.

It was in the closer hole, and I moved that to the farther hole and it doesnt seem to have made a difference.

Originally Posted by irishman999

My first question is, Do you see alot of black smoke when you mash on it? The Quadrajet is vacuum operated so it should not be dumping gasoline unless you have enough vacuum to open the secondaries. Is your carb the original one on your truck?

I know my engine is burning oil, so at start up there is some black smoke. At times I think that there is some black smoke but it just isn't enough to really tell. The secondaries are just floating, they do not have that vacuum operated linkage hooked up to them. The PO took it off because he said that they go bad and it works without it. I have the vacuum thing, but I do not have the actual linkage that goes between that and the secondaries. Could this be the problem?

The carb is the original one to the truck that I know of. I pulled this engine and carb out of a K20 that was all rusted, and put it in my k10.

[tucsonjwt]

When your truck is warmed up, remove the air cleaner and operate the throttle to simulate condition you describe above. On two of my squares, the Qjets had a sticky choke valve, causing the engine to bog and consume a lot of gas. These choke valves and associated linkage have a tendency to carbon up and stick. I had an Edelbrock that had a choke valve that was manufactured slightly too big for the opening in the carb - I had to remove the valve and file it off slightly - then the choke would never close off completely and caused hard cold starts. I would try a spray can of gumout to clean the carb when it is warmed up.l

[irishman999]

Originally Posted by Mattman2010

It was in the closer hole, and I moved that to the farther hole and it doesnt seem to have made a difference.



I know my engine is burning oil, so at start up there is some black smoke. At times I think that there is some black smoke but it just isn't enough to really tell. The secondaries are just floating, they do not have that vacuum operated linkage hooked up to them. The PO took it off because he said that they go bad and it works without it. I have the vacuum thing, but I do not have the actual linkage that goes between that and the secondaries. Could this be the problem?

The carb is the original one to the truck that I know of. I pulled this engine and carb out of a K20 that was all rusted, and put it in my k10.

If its burning oil the smoke should be a white/blue color, black=rich. Try connecting that vacuum pull off, That will keep the secondaries from flapping open before the vacuum condition is right.

When those secondaries open it pulls some needles out of the big secondary jets that dump fuel down your carburator.

I have to warn you that this is my theory, I am not an expert and there is most likely 100's of people here who are experts.

[nbpro]

http://www.73-87.com/7387garage/drivetrain/myqjet.htm

[danomano]

This might help

http://www.florida4x4.com/tech/quadrajet/

[Mattman2010]

I don't have one around here where I live, You have to call of the salvage yards and they will get the part for you. I am pretty sure the PO has a linkage I can use because I was asking him about it when I first pulled the engine and he said I dont need it.

[ray_mcavoy]

Originally Posted by Mattman2010

I am pretty sure the PO has a linkage I can use because I was asking him about it when I first pulled the engine and he said I dont need it.

Yeah, get that linkage and hook it back up. Sounds like the PO wan't very familiar with how QJets work.

They have mechanical secondary throttle blades with a set of "air doors" on top. The air doors open based on engine demand (the air flowing past them pulls them open). That vacuum can & linkage that the PO removed doesn't actually open the secondary air doors. Instead, it acts as a damper to keep them from opening too quickly. There's also a torsion spring that controls the opening rate.

The bog you're getting is a sure sign that the secondary air doors are opening too quickly because of the missing parts. The air doors also operate the secondary metering rods that irishman999 mentioned. With the missing parts, the air doors are likely opening too far (beyond engine demand) and in turn, pulling the secondary rods to the max rich position.

[motornut]

I second that,
and have made some temp linkages outa cut up bits of metal cloths hangers

Originally Posted by ray_mcavoy

Yeah, get that linkage and hook it back up. Sounds like the PO wan't very familiar with how QJets work.

They have mechanical secondary throttle blades with a set of "air doors" on top. The air doors open based on engine demand (the air flowing past them pulls them open). That vacuum can & linkage that the PO removed doesn't actually open the secondary air doors. Instead, it acts as a damper to keep them from opening too quickly. There's also a torsion spring that controls the opening rate.

The bog you're getting is a sure sign that the secondary air doors are opening too quickly because of the missing parts. The air doors also operate the secondary metering rods that irishman999 mentioned. With the missing parts, the air doors are likely opening too far (beyond engine demand) and in turn, pulling the secondary rods to the max rich position.

[gchemist]

PM with your e-mail address. I'll send a full basic Qjet pdf file to tune it.