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Stupid Carb....


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Ok, so I just replaced the intake manifold gaskets on my 87 GL (half of the drivers side one was completely gone, talk about a vacuum leak). Sealed up great. Well, because I had the leak all sealed up, I figured I could take the pennies off the throttle pedal, and try adjusting the carb. I tighten the mixture screw all the way down, then backed off 2.5 turns. Then I went to do the same with the speed screw, but it never tightened down. I went to start up the car, figuring I'd just adjust it from where it was. As soon as I started it, it acted like it had WOT. I shut it off just as it hit 4500rpm. :eek: So, I went and tighten the mixture screw all the way down, no change. Moved the choke plate, no change. I'm thinking it is something to do with that speed screw. Please help, I need my car back.

 

EDIT: Scratch that, the throttle is stuck part way open..... Any ideas why? I'll look at it more closely when I get home from work, but what would cause it to get stuck? And the issue is one the throttle, not the pedal.

Edited by Dj7291993
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Then I went to do the same with the speed screw, but it never tightened down. I went to start up the car, figuring I'd just adjust it from where it was. As soon as I started it, it acted like it had WOT. Scratch that, the throttle is stuck part way open..... Any ideas why? I'll look at it more closely when I get home from work, but what would cause it to get stuck?

 

Your "speed screw" is not supposed to be screwed in so far. The throttle is that way because of this. You have now bypassed the idle circuit and that is why the engine is not responding to adjustment of the mixture screw.

 

Set you idle mixture screw out 2 turns, then unscrew the air/fuel mixture screw, aka speed screw, some. Start you car and adjust the idle speed using the a/f mixture screw.

 

In the future, adjust your carb with the car running and don't change more than one thing at a time. Read up on setting lean best idle before you try optimizing for fuel economy.

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... Then I went to do the same with the speed screw, but it never tightened down. ...

 

That Screw is not supposed to be tightened like that.

 

So you must unscrew it (almost all the way out) and then Start the engine.

 

While the engine is Running you might adjust it to find the Right Idle speed... Should be ~ 800 RPM's.

 

Kind Regards.

Edited by Loyale 2.7 Turbo
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Yeah, I had a suspicion that was the problem, but figured I'd get input anyways. I'll be able to set it tomorrow (work stuff). I should've double checked, I was doing it off memory, and I've only done it once, it was a while ago (vacuum leak that big, and you can't open the idle circuit far enough). I wish they still taught carbs in school (I'm studying automotive). I understand why they don't, but there are still a lot out there, and since the only mechanic in my family lives in Iowa, I'm kinda on my own for finding the info.

 

Anyways, thanks guys. I'll check on that tomorrow. I'm hoping that fixing that vacuum leak will bring my millage back up, as right now, I'm at about 17mpg. I'd like to at least get back up to 22mpg, if not higher. Still kinda jealous of my dad's 88 GL w/ mpfi, 38mpg in that thing.

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