A/F Screw

[mike1346]

I cant find what the factory setting is for the A/F Screw on my carb. Anyone know how many turns out is factory? Does turning in the screw restrict air or fuel? Trying to dial in the carb and I have a feeling my A/F screw may be out of adjustment. I can put my hand partly over the airbox intake and restrict the aiflow and it seems to run better (just reving it while setting about 12k rpm near redline) when ever I put it in gear and take off it maxes out at 7-8k rpm. My theory is I'm restricting the air enough, but once I put a load on the motor (200 lbs of me) its not getting enough air. I've changed the "clip" on the needle valve to run lean and rich it seems to run better on the lean side (I'm about about 2-3k ft above sea level)

Thanks in advance
Mike

[SpudRider]

If the mixture screw is on the engine side of the carburetor, it's a fuel screw. If the mixture screw is on the airbox side of the carburetor, it's a air screw. Most 4-stroke engines have carburetors with fuel screws. Many 2-stroke engines have carburetors with air screws. Tightening the screw reduces intake, and loosening the screw increases the intake.

Where is your mixture screw located?

Spud

[mike1346]

The one I'm pretty sure is the A/F screw is between the carb and engine in front of the fuel bowl at just the right angle unless you have a screw driver 1/2" long or a special tool it's hard to adjust while on the motor.

[Weldangrind]

The fuel screw (or pilot screw) only comes into play once you open the throttle. It is responsible for the transition from the idle jet to the main jet. If you need to open the screw more than two turns for a smooth transition, the slow jet is either clogged or too small.

[mike1346]

Originally Posted by Weldangrind

The fuel screw (or pilot screw) only comes into play once you open the throttle. It is responsible for the transition from the idle jet to the main jet. If you need to open the screw more than two turns for a smooth transition, the slow jet is either clogged or too small.

Thanks "Spud" & "Weld" so is the "slow jet" the idle or main jet or is there a 3rd jet hiding? 8O

And is 2 turns out on the A/F the standard for factory jets?

[Weldangrind]

You have a slow jet / idle jet (very tiny, like 0.20mm ID), a main jet (probably 1mm ID) and a pilot mixture screw. The jets are located inside the carb, and are revealed upon removing the float bowl.

The pilot screw is normally 1.5 turns out, but you need to adjust to suit your bike and elevation.

[mike1346]

Originally Posted by Weldangrind

You have a slow jet / idle jet (very tiny, like 0.20mm ID), a main jet (probably 1mm ID) and a pilot mixture screw. The jets are located inside the carb, and are revealed upon removing the float bowl.

The pilot screw is normally 1.5 turns out, but you need to adjust to suit your bike and elevation.

Cool thanks "Weld"

[SpudRider]

As I expected, it appears your Pilot Mixture Screw (PMS) is a fuel screw. In this case, tightening the screw reduces fuel and leans the fuel/air mixture. Loosening the screw increases fuel and enriches the fuel/air mixture. As Weld stated, the PMS is outside the carburetor, and the fuel jets are located inside the carburetor.

Spud