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Air Screws

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Guest

Guest
Can anyone tell me on the BS CV Carbs do the Air Screws just put more air in the fuel mix. Or is it more fuel too.
 
Its a measured orifice that limits the rate at which fuel flows from the bowls through the main jet.

almost like the little valve on a gas can that allows gas to pour but at a measured rate.

Perhaps these need to be changed with larger main jets to allow the larger jet to work properly.
 
JEEPRUSTY said:
Its a measured orifice that limits the rate at which fuel flows from the bowls through the main jet.

almost like the little valve on a gas can that allows gas to pour but at a measured rate.

Perhaps these need to be changed with larger main jets to allow the larger jet to work properly.
Click to expand...

No disrespect intended but this is wrong.

The pilot (sometimes called the "air") screws allows an emulsion of fuel and air to enter the air flow which controls the mixture at idle and slightly above. More turns open means more emulsion (fuel) enters.
 
Nessism said:
No disrespect intended but this is wrong.

The pilot (sometimes called the "air") screws allows an emulsion of fuel and air to enter the air flow which controls the mixture at idle and slightly above. More turns open means more emulsion (fuel) enters.
Click to expand...


These are not adjustable on some carbs
how do you adjust them on yours?

Theres is a pilot air and a main air jet
I was refering to the mains.

again i was makin an analogy and if the amount of air was not contolled then the flow would be erratic.

it is usd because the carbs cant literally suck the fuel out of the bowls its is drawn off

A cutaway diagram would show it clearly

no disrepsect
 
Hi,

The VM series of carbs on the older GS bikes have separate fuel and air mixture screws.

The newer CV style carbs (BS series) have a single "idle mixture" screw under a cap on the top front of the carbs.

reassembly040410_01-1.jpg


You must remove the caps covering the mixture screws in order to adjust them. Turning the mixture screws out increases the fuel at idle.


Thank you for your indulgence,

BassCliff
 
Last edited:
BassCliff said:
Hi,

The VM series of carbs on the older GS bikes have separate fuel and air mixture screws.

The newer CV style carbs (BS series) have a single "idle mixture" screw under a cap on the top front of the carbs.

reassembly040410_01-1.jpg


You must remove the caps covering these screws in order to adjust them. Turning the mixture screws out increases the fuel at idle.


Thank you for your indulgence,

BassCliff
Click to expand...
So the Air screws, only effect the idle? nothing to do with mid or high range RPM.:confused:
 
mike10 said:
So the Air screws, only effect the idle? nothing to do with mid or high range RPM.:confused:
Click to expand...

Hi,

Generally speaking, yes, the idle circuit and pilot jet are in play up to about 1/4 throttle. Jet needle for midrange and main jet for WOT. See http://www.iwt.com.au/mikunicarb.htm .

"Air screw" is the wrong term.


Thank you for your indulgence,

BassCliff
 
Last edited:
Huh???

Huh???

JEEPRUSTY said:
These are not adjustable on some carbs
how do you adjust them on yours?

Theres is a pilot air and a main air jet
I was refering to the mains.

again i was makin an analogy and if the amount of air was not contolled then the flow would be erratic.

it is usd because the carbs cant literally suck the fuel out of the bowls its is drawn off

A cutaway diagram would show it clearly

no disrepsect
Click to expand...



This is total, 100% nonsense!
 
Last edited:
Good Carb web site

Good Carb web site

BassCliff said:
Hi,

Generally speaking, yes, the idle circuit and pilot jet are in play up to about 1/4 throttle. Jet needle for midrange and main jet for WOT. See http://www.iwt.com.au/mikunicarb.htm .

"Air screw" is the wrong term.


Thank you for your indulgence,

BassCliff
Click to expand...
A lot of good info even I can understand. Carbs used to really scare me. The more I learn about them, the better friends we are becoming. :D
 
There are pilot air jets and main air jets on the BS carbs too.

I was wondering if anyone has had to replace the springs in the CV's because they are out of spec. I don't even know what the free length is supposed to be. Anyone know? :confused:

Would a collapsed spring cause a lean condition @ 1/8 throttle?
 
Hi,

Yes, there are air jets. But as I understand these carbs, they are not adjustable.

Mikuni BS32SS Carb Manual

The above manual has your cutaway views.


Thank you for your indulgence,

BassCliff
 
BassCliff said:
Hi,

Yes, there are air jets. But as I understand these carbs, they are not adjustable.

Mikuni BS32SS Carb Manual

The above manual has your cutaway views.


Thank you for your indulgence,

BassCliff
Click to expand...
Then would the air screw adjustment being too rich or lean, effect the mid or high RPM ranges? After I shimmed my needles I thought I needed to close down the air screws some but I ended up opening them back to where they were.
 
mike10 said:
Then would the air screw adjustment being too rich or lean, effect the mid or high RPM ranges? After I shimmed my needles I thought I needed to close down the air screws some but I ended up opening them back to where they were.
Click to expand...

Hi,

What you are calling the "air screw" (on a CV carb) is actually the "idle mixture screw" and controls the amount of fuel in the idle circuit, at idle or just off idle. It affects the other circuits very, very little.

While there is a little overlap, the circuits are independent of each other. It is quite possible to be too rich on one circuit and too lean on another. Plug chops can tell you the whole story.

Thank you for your indulgence,

BassCliff
 
That explains a lot

That explains a lot

BassCliff said:
Hi,

What you are calling the "air screw" (on a CV carb) is actually the "idle mixture screw" and controls the amount of fuel in the idle circuit, at idle or just off idle. It affects the other circuits very, very little.

While there is a little overlap, the circuits are independent of each other. It is quite possible to be too rich on one circuit and too lean on another. Plug chops can tell you the whole story.

Thank you for your indulgence,

BassCliff
Click to expand...
Before I did the Carb needle shims, I kept fooling with the airscrews and wondering why my Mid range power wasn't smoothing out. Below 3500 RPM ok and above 5000 ok. It didn't like running between 50 and 70 MPH.
 
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