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640 running too rich
#1
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jimw
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I can't seem to get my carburetor to run leaner. The only adjustment I am aware of is the air valve which I have adjusted according to the book. While the engine is idling, the air valve is slightly open. Depressing it a little more makes the engine run a little faster, depressing it even more make the engine start to falter as does closing it completely. Any ideas?

Posted on: 9/25 12:55
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Re: 640 running too rich
#2
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Tim Cole
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That's about all you can adjust on that unit. If the car is running rich at idle there is blow off tube that is supposed to prevent that. If it is clogged the idle will be rich.

The next area is the float. When those needles and seats become worn they are a problem. The needle doesn't seat and gas flows all over the place. As well, sometimes the float doesn't seat because it hits the cover. And if the seams crack, the float fills with gasoline and doesn't.

Next is fuel delivery. That carburetor is designed for the vacuum tank. If that isn't being used a needle and seat designed for non-gravity feed needs to be installed.

Is Classic Carburetors in Arizona still around? The only other source I knew isn't alive anymore.

Posted on: 9/25 20:25
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Re: 640 running too rich
#3
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jimw
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Tim

Thanks for the input. Where is the "blow off" tube. All I can see is the primary air intake and the air valve as air intakes. Is the blow off tube you are talking about the venturi around the main jet?

Posted on: 9/25 21:14
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Re: 640 running too rich
#4
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Tim Cole
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I'm sorry, on that unit I believe it is internal. Look for a passage above the throttle plate. It acts essentially as an idle jet and meters fuel into the engine that would otherwise collect below the throttle causing the motor to gradually go super rich at idle.

So if your car starts out okay and then loads up at idle, maybe that is your problem.

Posted on: 9/26 11:23
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Re: 640 running too rich
#5
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jimw
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Here is a cross section picture of the carb. Where is this passage?

Attach file:



jpg  IMG_5154.JPG (3,500.02 KB)
1238_633207100c283.jpg 4608X3456 px

Posted on: 9/26 15:09
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