1978 Q Jet Air / Fuel tunning

[Rude Boy]

On my 1978 GMC Jimmy I'm looking for someone here in AZ, who can get this QJet dialed in for me. I had it rebuilt last weekend, and the guy who rebuilt it was supposed to tune it in for me, but he is out of town. Can someone help me find somebody who can actually work on these?

[C-10 simplex]

Where is mariacopa?

2) You could try doing it yourself provide you stay away from the fan.

[Rude Boy]

Maricopa, Arizona. I tried doing it myself, but I could not keep it running to tune the air and fuel. The fan will be a major problem from what I can see.

[C-10 simplex]

So did the engine stay running before the rebuild?

[Rude Boy]

Yea, it ran good for about two miles, then it would start to suck in air through the top gasket. So I got the whole thing rebuilt to be on the safe side.
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[C-10 simplex]

So this means that it is not an ignition problem.

Do you know where the fast idle and curb idle screws are on this carb?

[Rude Boy]

The only adjustments that I made to it was the two screws in the front on the lower left and right. Other than than that I have no clue.

[C-10 simplex]

What, exactly, did you do to the front 2 screws?

i wish someone else would drop in the thread; i am mentally incapacitated at the moment for reasons i don't wish to get into publicly at the moment. And i apologize for possibly having to drop out of the discussion.

[C-10 simplex]

You may want to try youtube for some instructional videos.

When you first start the engine, what is your procedure?

[Rude Boy]

When I installed the carb, the screws were all the turned to the right, which is no gas or air. I turned each screw 3 complete turns to the left. When I go to start it, I don't give it any gas until after 5 seconds. Next I give the gas pedal very quick hits until it starts to run. Then I have to keep the pedal all the way down to keep it running, but it smokes. If I take my foot off the gas, it dies. I tried opening up the screws more, but with no luck.
I understand that you are frustrated with my problem, so I will check out YouTube.
Posted via Mobile Device

[Rude Boy]

When I installed the carb, the screws were all the turned to the right, which is no gas or air. I turned each screw 3 complete turns to the left. When I go to start it, I don't give it any gas until after 5 seconds. Next I give the gas pedal very quick hits until it starts to run. Then I have to keep the pedal all the way down to keep it running, but it smokes. If I take my foot off the gas, it dies. I tried opening up the screws more, but with no luck.
I understand that you are frustrated with my problem, so I will check out YouTube.
Posted via Mobile Device
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[C-10 simplex]

No, i'm not really frustrated with your problem; i've got my own problems on my plate that i have to deal with.


i don't think turning the idle mix screws out 3 turns is necessarily the best way to tune. Do you have a vacuum gauge?

Do you know where the fast idle screw is under the choke housing?

What about the regular idle screw at the throttle arm?

So, you are saying you don't touch the gas pedal when you start?

[ray_mcavoy]

Originally Posted by Rude Boy

When I installed the carb, the screws were all the turned to the right, which is no gas or air. I turned each screw 3 complete turns to the left.

Since the rebuilder left the screws turned all the way in, you're on the right track with backing them out like that to get a baseline starting point. 2 to 3 turns out should get you to the point where it will at least stay running on it's own provided that the idle speed isn't adjusted too low.

When I go to start it, I don't give it any gas until after 5 seconds. Next I give the gas pedal very quick hits until it starts to run. Then I have to keep the pedal all the way down to keep it running, but it smokes. If I take my foot off the gas, it dies. I tried opening up the screws more, but with no luck.

That sounds like either a problem with the choke or an internal carb problem (like a float that's adjusted too high) that's causing it to run too rich. To rule out the choke, you can temporarily tie it open for troubleshooting purposes.

[69gmcc10]

Originally Posted by Rude Boy

When I installed the carb, the screws were all the turned to the right, which is no gas or air. I turned each screw 3 complete turns to the left. When I go to start it, I don't give it any gas until after 5 seconds. Next I give the gas pedal very quick hits until it starts to run. Then I have to keep the pedal all the way down to keep it running, but it smokes. If I take my foot off the gas, it dies. I tried opening up the screws more, but with no luck.
I understand that you are frustrated with my problem, so I will check out YouTube.
Posted via Mobile Device

3 turns out is allot! 1.5 turns from closed is a good starting point.

[Rude Boy]

Wow! I will take your advise and give it a shot. First I will close them, then open 1.5 turns, and see what that does. Second I will open the choke all the way to see what happens. If all else fails, then I will send it to a Real Hot Rod Shop. Thanks for your advise!

[C-10 simplex]

Well, really i think the choke needs to be closed for this to work right; So when you start it, you don't touch the gas?

If you don't then the carb is not set on high idle, this may be in part causing the stalling.

You got a tach?

[Rude Boy]

At first I never give it gas. I don't have one. How can I fix that?
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[C-10 simplex]

If the engine is cold(hasn't been run for at least 2 hrs) you're generally supposed to press the pedal down and release----this closes the choke blade and squirts fuel into the intake. Also, when the choke blade closes, this also puts the fast idle cam onto high step---should be around 1200 rpm or so.

This closing of the choke should help starting and running for the first 30 seconds or so, although in arizona i'm not sure how much it would help.......
Also, being on hi-step should help to keep the engine running while the engine is cold, still trying to warm up.

What you can do, when the engine is cold, is to manual move the throttle lever and see if the choke snaps shut.

This would all be easier if i could show pictures, but i'm unable to at the moment.

[GASoline71]

Also... make sure your timing is dialed in right. Lots of "carb" propblems end up being a combination of carb, ignition, and timing.

Gary

[cableguy0]

If putting the pedal to the floor barely gets the engine running you have more serious issues than the idle mixture screws are going to deal with. The two screws in front are the idle mixture screws and have 0 effect on the way the engine runs once your on the throttle. If its chugging,puffing black smoke and wont run the engine is flooding. I would be very suspect of float level especially on a fresh rebuild.