Air Screw or Not Air Screw

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phliparoonie
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Air Screw or Not Air Screw

Post by phliparoonie » Wed Feb 22, 2017 6:55 pm

Several times on this forum I have come up against confusion over the function of the "1-1/2 turns out from soft seat" screw on the Keihin CVK32 carb. I always thought since this screw is outside the fuel bowl and just before the cylinder, that its function was to meter air into the fuel mix: screw it out to add more air (leaner), screw it in to add less air (richer). Other posters here have said, "Nope, that's a fuel mix screw" or "if it's next to the jug it's fuel, if it's on the other side of the carb, it's air", "It only adjust the air at idle" etc. Even the Keihin website is a little confusing because there is an adjustment to the idle circuit INSIDE the fuel bowl, and their text call that an idle mixture screw AND it call the screw I'm talking about an idle mix screw. Confused yet :?

Now, the only thing I know about engines is what I have learned here over the past four years, and only on this, my first bike ever. I don't consider myself any kind of expert on any mechanical aspect of these rigs. Having said that, just looking at the setup convinces me that this is an air screw. Attached are pics of the left carb. If I am completely bass-ackwards on this assertion, please clue me in.
Keihin CVK32 air mix screw_01.JPG
Keihin CVK32 air mix screw_02.JPG
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Re: Air Screw or Not Air Screw

Post by Buckhorn » Wed Feb 22, 2017 7:28 pm

From the Best of Section on the forum. There's also a link in there somewhere to a site that explains the operation of the CVK carb.
Pete
Air/fuel screw factory turnout: 1 1/2 from soft-set. Soft-set: The air/fuel mixture-adjustment screw is turned very gently CW until you just meet resistance (soft-set), any further and you will damage the needle.

:idea: Ural’s Keihin OEM factory carbs have an "fuel" screw, e.g. CW/IN lean, CCW/OUT rich
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Re: Air Screw or Not Air Screw

Post by chaos2 » Wed Feb 22, 2017 8:22 pm

The idle adjustment screw meters fuel for the idle circuit, this cutaway is from a Harley Keihin but basically the same. Unscrewing ( F in the drawing) allows more fuel into the mix.
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Re: Air Screw or Not Air Screw

Post by BillyG » Wed Feb 22, 2017 8:32 pm

You are...a$$ backwards. If the screw is on the air INTAKE side of the carb it is a "air screw". Then CW/In is rich and CCW/Out is lean. If the screw is on the OUT FLOW side of the carb it is a mixture screw. In this case CW/IN is lean and CCW/Out is rich.

The Keihin screw only affects the idle circuit (white lie)...hence it is a "idle mixture screw". After 1/4-1/3 throttle the needle and main jet take over.

Either one, 9 times out of 10, the factory default settings is lightly seated and 1&1/2 turns out. Maybe 8 times out of 10. Possibly 7. When in doubt...50/50 ;-)
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Re: Air Screw or Not Air Screw

Post by gobium » Wed Feb 22, 2017 8:46 pm

:lol: Ha!

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Re: Air Screw or Not Air Screw

Post by gobium » Wed Feb 22, 2017 8:56 pm

On video
Goto
7:11

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Re: Air Screw or Not Air Screw

Post by rougaroo » Wed Feb 22, 2017 9:05 pm

And the first part of this: http://www.sovietsteeds.com/forums/view ... +air+screw

In the video Van posted starting at 4:03 or thereabouts you can see how it works.

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Re: Air Screw or Not Air Screw

Post by gobium » Wed Feb 22, 2017 9:56 pm


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Re: Air Screw or Not Air Screw

Post by phliparoonie » Thu Feb 23, 2017 7:25 am

:bow: Thanks to all for the insight and clarification. I did not know there was a channel from the fuel bowl to that tiny orifice. I feel better already. :cheers:
It is important to keep an open mind. But not so much that your brain falls out. Carl Sagan
I am old, but I'm happy. Cat Stevens
It's a tractor, not a Ferrari. Holopaw Gene

2004 Tourist "Charlie" 25,036 km - 18/04/24
stock: pipes, carbs, airbox, fuel petcock, tractor seat
new/add: windscreen,hack headlight,4 head stud holes,pistons,rings,starter,FD splined hub,clutch actuator bearing, clutch arm,donut,drive shaft,Ducati ignition,tank xover dscnect

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Re: Air Screw or Not Air Screw

Post by rougaroo » Thu Feb 23, 2017 12:20 pm

And for those of you are truly obsessive - you know who you are - there is this:
Image

available here: https://cv-performance.com/ez-just-mixture-screw

Even though it isn't listed for the CVK32, it fits.

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Re: Air Screw or Not Air Screw

Post by Wildhorse Cafe » Thu Feb 23, 2017 1:21 pm

Good video:



Bad video:


been down that rabbit hole. :lol:
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Re: Air Screw or Not Air Screw

Post by gobium » Thu Feb 23, 2017 4:33 pm

phliparoonie wrote::bow: Thanks to all for the insight and clarification. I did not know there was a channel from the fuel bowl to that tiny orifice. I feel better already. :cheers:
It is not!
Gas does not come out at the tiny orfice mixture screw

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Re: Air Screw or Not Air Screw

Post by gobium » Thu Feb 23, 2017 4:35 pm

ARE WE ALL CONFUSED NOW? :lol:

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Re: Air Screw or Not Air Screw

Post by phliparoonie » Fri Feb 24, 2017 7:35 am

gobium wrote:ARE WE ALL CONFUSED NOW? :lol:
:lol: YES! Why you do dat? :?
It is important to keep an open mind. But not so much that your brain falls out. Carl Sagan
I am old, but I'm happy. Cat Stevens
It's a tractor, not a Ferrari. Holopaw Gene

2004 Tourist "Charlie" 25,036 km - 18/04/24
stock: pipes, carbs, airbox, fuel petcock, tractor seat
new/add: windscreen,hack headlight,4 head stud holes,pistons,rings,starter,FD splined hub,clutch actuator bearing, clutch arm,donut,drive shaft,Ducati ignition,tank xover dscnect

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Re: Air Screw or Not Air Screw

Post by Peter Pan » Fri Feb 24, 2017 11:11 am

I still do not get it right...so what is the real function and adjustment.
This is the only part of my rig where I continue confused after nearly 4 years still.
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