Adjusting Mixture Level on 86-87 Carb - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 11-15-2002, 08:38 PM Thread Starter
 
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Adjusting Mixture Level on 86-87 Carb

K.. According to the Chilton manual I require a Carbon Monoxide exhaust gas analyzer. The steps seem pretty involved but nothing I can't figure out. My question is this.... I know that sometimes in manuals there are steps that don't need doing or there are other simpler ways. I need a simpler way to adjust the idle mixture. Can anyone tell me how to for an 86 Carburator?

Thanks
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post #2 of (permalink) Old 11-16-2002, 08:26 AM Thread Starter
 
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Re: Adjusting Mixture Level on 86-87 Carb

Anyone?
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post #3 of (permalink) Old 11-16-2002, 09:03 AM
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Re: Adjusting Mixture Level on 86-87 Carb

The idle mixture screw is on the pass. side of the carb, up inside a hole that has a pin across it so you can't "tamper" with it. You have to remove the carb from the manifold to drive the pin out. Then you can adjust the screw with a small flat-blade screwdriver. Let the motor warm up to normal operating temperature, then turn the screw clockwise until the RPM's fall off (too lean). Back it out until the RPM's pick up and the idle smooths out. Then turn it back in just a shade and it should be right. HTH
Here is a picture. The mixture screw is in the hole in the lower center part of the pic. You can see the pin that was tapped out of the way.
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post #4 of (permalink) Old 11-16-2002, 10:17 AM
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Re: Adjusting Mixture Level on 86-87 Carb

LIL', what type of carb is on your truck? Is it an Aisin or an Hitachi? Do you have bolts or studs holding it to the manifold?
post #5 of (permalink) Old 11-16-2002, 11:15 AM Thread Starter
 
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Re: Adjusting Mixture Level on 86-87 Carb

K.... That is what I read in the Chilton manual. My only concern is that you wouldn't know if the mixture you are setting it to is correct. How would you know without the Carbon Monoxidye Exhaust gas analyser that they mention in the book. Is a guess good enough? Can I damage the engine from running too lean.? Can I buy this tool anywhere?
Don't want to try and guess just to find I have damaged the engine.

Thanks for your words of wisdom but it seems I will need some more.
[img]images/graemlins/smirk.gif[/img]
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post #6 of (permalink) Old 11-16-2002, 11:52 AM
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Re: Adjusting Mixture Level on 86-87 Carb

Exhaust analyzers are in the thousands of dollars, hardly seems worth the purchase to tune the Zuk!!! Many garages have them already, so your best bet would be to take it in and have them tune it while hooked up to the machine. They shouldn't charge too much for this.
post #7 of (permalink) Old 11-16-2002, 12:28 PM
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Re: Adjusting Mixture Level on 86-87 Carb

You won't damage the engine by turning this screw. Your objective is to get the smoothest idle, then lean it just a bit. It won't be a "guess", it will be darn close to perfect. You shouldn't have to turn it more than 1/2 turn in either direction to get it right. It's easy to tell if it's too lean because the idle will be rough. In any case, if it's not "perfect" it won't hurt your engine, it will only increase emissions. You'll find out for sure when you have it inspected and they use the Exhaust Gas Analyzer on it.
IMO, it's better to do this adjustment yourself rather than letting a shop do it. They probably won't take the time to remove that "tamper-proof" pin. They will more likely tell you that the carb is "sealed" or "computerized" and cannot be adjusted. Or worse, they'll charge you money and do nothing at all (Or does that kind of thing only happen to me? [img]images/graemlins/wink.gif[/img])
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post #8 of (permalink) Old 11-16-2002, 01:56 PM
 
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Re: Adjusting Mixture Level on 86-87 Carb

You don't have to guess or use an analyser. When they use the analyser, they tune it on
the lean side typically, to meet emmissions. You can use a tach to do the same thing. You
tune it to the highest idle, Then lean it a tiny bit by closeing it maybe 1/8 turn (It's bleeding
fuel, not air, behind the throttle plates.) A shop dwell/tach is useful for this as they usually
have a low RPM range just for doing this. A range of 0-1200 RPM or so, on most I have seen.

Also keep in mind. this is an IDLE circuit adjustment. Above an idle, it has no effect at all.
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post #9 of (permalink) Old 11-16-2002, 02:34 PM Thread Starter
 
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Re: Adjusting Mixture Level on 86-87 Carb

K I don't understand this from MrSurly...

"in any case, if it's not "perfect" it won't hurt your engine, it will only increase emissions"

How does lean in out create higher emissions. I have been told again and again the lean is less emissions.
I will make the attempt tomorrow. I hope it will go smoothly.

Thanks for all the suggestions

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post #10 of (permalink) Old 11-16-2002, 03:15 PM
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Re: Adjusting Mixture Level on 86-87 Carb

Running too lean CAN cause the engine to run too hot. this in turn can result in high NOx gas reading. Generally, it is the rich condition that gets you into trouble with the e-test. Too much fuel (HC) equals too cool of a cylinder and not a full, efficient burn process. This causes high HC (fuel) and CO (carbon monoxide) levels on an e-test. Did you figure out which carb you have yet?? Do you have a Converter? Aisin(bolts)/Hitachi(studs).
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