Adjusting Idle Mixture on a CV carb
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From: Ft.Worth, Texas
Adjusting Idle Mixture on a CV carb
If the idle mixture screw has to be set to 3 1/2 turns from bottom for maximum RPM at idle, does that indicate that the carb jetting is too large or too small ?
Road Master
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From: Ghent NY
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From: Ft.Worth, Texas
Thanks. Ive read that page a few times but it doesnt explain mixture screw position relative to jet size. I want to know what influences the number of turns the mixture screw is set for maximum RPM at idle. Is it rich jetting or lean jetting? My guess is that a larger primary jet will require more turns out of the mixture screw . What I am trying to achieve is a balance of maximum performance and maximum fuel mileage.
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From: Poolville
Not a cv carb guy but i would think out would be to small or you have a vacuum leak. But i have heard of 3 to 3 1/2 turns as acceptable. If it's running ok don't worry about it. Ride...
Road Master
Joined: Jan 2013
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From: Ghent NY
Your not really looking for Max RPM's at idle. You want to be at mid point with the screw between where its cranked in and bogs or stumbles and where it does the same with it turned out. If it don't stumble when turned in you need to go smaller on the low speed jet.
Like 98hotrod said 3 to 3.5 is acceptable on the upper end of the setting
your guess of that a larger primary jet will require more turns out of the mixture screw is backwards. if your out 3.5 turns now you could drop a jet low speed jet size
Like 98hotrod said 3 to 3.5 is acceptable on the upper end of the setting
your guess of that a larger primary jet will require more turns out of the mixture screw is backwards. if your out 3.5 turns now you could drop a jet low speed jet size
Last edited by Ruggs59; Nov 13, 2015 at 08:53 AM.
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From: Upstate New York
The Keihin CV idle mixture screw controls fuel. More turns out=more fuel=richer. The Mikuni HSR idle mixture screw controls AIR. More turns out=more air=leaner.
If your mixture screw is too far out, your CV carb would need a larger pilot jet.
You don't tell us what size pilot jet you have now, or what else is you have (air cleaner, pipes, etc.).
If your mixture screw is too far out, your CV carb would need a larger pilot jet.
You don't tell us what size pilot jet you have now, or what else is you have (air cleaner, pipes, etc.).
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From: Ft.Worth, Texas
The Keihin CV idle mixture screw controls fuel. More turns out=more fuel=richer. The Mikuni HSR idle mixture screw controls AIR. More turns out=more air=leaner.
If your mixture screw is too far out, your CV carb would need a larger pilot jet.
You don't tell us what size pilot jet you have now, or what else is you have (air cleaner, pipes, etc.).
If your mixture screw is too far out, your CV carb would need a larger pilot jet.
You don't tell us what size pilot jet you have now, or what else is you have (air cleaner, pipes, etc.).
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Road Master
Joined: Jan 2008
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From: Montgomery, AL
I'd run the 46. Great info. Keep us posted.
Actually that is the slow jet. The main is like 180. My bike uses the 88 Sportster needle with no shims. A 45 slow jet and a 180 main. The motor is pretty much stock except for pipe and air cleaner. Approx 23/4 turned out idle screw.
Actually that is the slow jet. The main is like 180. My bike uses the 88 Sportster needle with no shims. A 45 slow jet and a 180 main. The motor is pretty much stock except for pipe and air cleaner. Approx 23/4 turned out idle screw.
Last edited by 92Fatty; Nov 13, 2015 at 06:20 PM. Reason: more info.
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