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05-16-2024, 06:35 PM | #1 |
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Idle Mixture Screw
I swapped out my carburetor for a rebuilt one, and I’m trying to adjust it. I’m a newbie at this. I’ve been working through the Les Andrews book, but I’m still unsure which direction is more lean and which direction is more rich for the idle mixture screw.
I’m thinking counter clockwise would make the mixture more rich. Do I have this backwards? Sent from my iPhone using Tapatalk |
05-16-2024, 06:58 PM | #2 |
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Re: Idle Mixture Screw
shew01: the idle mixture screw is an air bleed adjustment. Opening (CCW) the idle mixture screw allows more air to mix with the fuel and closing (CW) it decreases the amount of air in the fuel mixture, Hope this clears things up.
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05-16-2024, 07:44 PM | #3 | |
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Re: Idle Mixture Screw
Quote:
Thanks. I’ll be really frank. I don’t see much difference between fully closed and three turns open. This carburetor was rebuilt by a well known rebuilder on this forum; so, I’m assuming it was rebuilt correctly. Maybe I’m doing something wrong… Sent from my iPhone using Tapatalk |
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05-16-2024, 07:58 PM | #4 |
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Re: Idle Mixture Screw
That usually indicates a vacuum leak.
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05-16-2024, 08:00 PM | #5 |
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Re: Idle Mixture Screw
Or a worn throttle shaft.
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05-16-2024, 08:35 PM | #6 | |
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Re: Idle Mixture Screw
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05-16-2024, 08:39 PM | #7 | |
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Re: Idle Mixture Screw
Quote:
As soon as the engine RPM gets above about 500 to 600 RPM, the main jets start kicking in and the idle mixture screw doesn't really do anything (but the GAV will). I hope this helps. I start out with the mixture screw open 1-1/2 turns and make small adjustments from there.
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05-16-2024, 08:39 PM | #8 | |
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Re: Idle Mixture Screw
Quote:
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05-16-2024, 08:42 PM | #9 |
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Re: Idle Mixture Screw
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05-16-2024, 08:44 PM | #10 | |
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Re: Idle Mixture Screw
Quote:
Yes, I did start at 1-1/2. I need to check on a possible vacuum leak. Sent from my iPhone using Tapatalk |
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05-16-2024, 08:51 PM | #11 | |
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Re: Idle Mixture Screw
Quote:
I’ve had the car for almost 5 years, and the GAV never has done much; the car always ran fine without having to adjust the GAV. (That had me scratching my head because I’ve read quite a number of posts about setting GAV.) The carburetor has been on the car since I bought it until I swapped it for this rebuilt one today. I swapped the carburetor because of a leak while parked—that leak has been growing worse lately. According to my tachometer, the idle is set around 525. The car wants to stall randomly while stopping when set lower. I’m not sure if that is a float level issue or not. The old carburetor didn’t seem to have that problem. Yes, I started at 1-1/2 turns out. Sent from my iPhone using Tapatalk |
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05-16-2024, 08:52 PM | #12 | |
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Re: Idle Mixture Screw
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Thanks for the link. Sent from my iPhone using Tapatalk |
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05-16-2024, 09:34 PM | #13 |
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Re: Idle Mixture Screw
My vacuum wiper supply line was a very small copper line, it cracked near the manifold and caused issues. I just removed the fitting into the manifold and plugged it !
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05-17-2024, 08:36 AM | #14 | |
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Re: Idle Mixture Screw
Quote:
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05-17-2024, 11:24 AM | #15 | |
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Re: Idle Mixture Screw
Quote:
Yeah, I missed that. It’s a Zenith. Thanks for pointing that out. Sent from my iPhone using Tapatalk |
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05-17-2024, 02:56 PM | #16 |
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Idle Mixture Screw
There may be a slight vacuum leak in the wiper. When I warmed up the engine and idled at 500, I took this video. Is this helpful? This video is with the idle mixture screw 1-1/2 turns open. With the wiper disconnected and the vacuum gauge connected directly to the manifold, I could hear a difference in idle when the idle mixture screw was turned.
https://youtu.be/JeYbABtRKp0 Sent from my iPhone using Tapatalk Last edited by shew01; 05-17-2024 at 03:26 PM. |
05-17-2024, 03:10 PM | #17 |
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Re: Idle Mixture Screw
This is 3 turns open.
https://youtu.be/pzpxulmkFEQ?feature=shared Sent from my iPhone using Tapatalk |
05-17-2024, 03:19 PM | #18 |
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Re: Idle Mixture Screw
The wiper vacuum line itself does not seem to have a leak. I don’t know how to test the wiper body itself. This is 3 turns open measured at the wiper vacuum line at the wiper body.
https://youtube.com/shorts/nW-BxHJIy...NodHCP3DoLur1Q Sent from my iPhone using Tapatalk |
05-18-2024, 08:48 AM | #19 |
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Re: Idle Mixture Screw
Put a length of "wiper hose" on the wiper motor, suck on the other end.
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05-18-2024, 09:04 AM | #20 |
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Re: Idle Mixture Screw
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