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Old 10-22-2013, 02:21 PM   #1
sigpe57 OP
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Bing CV idle mixture screw question

"On the Bing CV carbs, the mixture circuit is a fuel circuit, so turning counter-clockwise will yeild a richer mixture."

Read this statement on web. Is it correct?
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Old 10-22-2013, 02:40 PM   #2
SOLO LOBO
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http://www.omnilex.com/public/bmw78/cvcarb.pdf


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Old 10-22-2013, 02:44 PM   #3
Plaka
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Quote:
Originally Posted by sigpe57 View Post
"On the Bing CV carbs, the mixture circuit is a fuel circuit, so turning counter-clockwise will yeild a richer mixture."

Read this statement on web. Is it correct?
Kinda. it's messy.

For your idle screw the idle jet sets the mixture. The gas it allows is mixed with some air to form a bubbly air/fuel mix. The idle mix screw itself then meters how much of this stuff gets into the airstream headed off to the intake valve, so in that sense it sets the idle mixture.

but your throttle stop screws also set the idle mix. They control how open the throttles are at idle. The slide isn't to active yet so you are just controlling idle air. This in turn affects how much of the idle mix is pulled, up to the limit the idles mix screw is holding.
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Old 10-22-2013, 02:44 PM   #4
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Quote:
Originally Posted by sigpe57 View Post
"On the Bing CV carbs, the mixture circuit is a fuel circuit, so turning counter-clockwise will yeild a richer mixture."

Read this statement on web. Is it correct?
Yep, not to be confused with the throttle stop screw which controls when the butterfly opens.
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Old 10-22-2013, 02:48 PM   #5
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That is a good article on Bings. And yep, idle mixture is a fuel adjustment.

Its a general rule, but not 100% so, that idle mixture screws downstream of the butterfly/slide will be fuel adjusting screws and counterclockwise will be richer. Conversely idle mix screws upstream of the butterfly/slide will be air screws and counterclockwise leans the mixture out.
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Old 10-22-2013, 03:49 PM   #6
sigpe57 OP
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If you unscrew the idle mixture screw, will the fuel pour out?

I can always try it but asking is less messy.
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Old 10-22-2013, 03:55 PM   #7
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I don't think so - been a long time since I had to do it. BUT.... every time you screw it all the way out the o-ring on the needle gets roughed up a little coming out through the threads. And that o-ring is kind of important to ensure the absence of air leaks into fuel mix screw.
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Old 10-22-2013, 04:40 PM   #8
Plaka
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Originally Posted by sigpe57 View Post
If you unscrew the idle mixture screw, will the fuel pour out?

I can always try it but asking is less messy.
The reservoir of fuel is in the bowl, below the idle jet. The circuit depends on airflow both to provide the bubbles for the initial mix and the flow for the final mix through the screw. Probably something in the passage that will drip out.

Cuts up the o-ring. Only do if you gotta.
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