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How to Adjust the Air Mixture in a Carburetor

by Zyon Silket

The carburetor on a motorcycle has an air/fuel mixture screw to adjust the amount of air going to the engine. If you reset a carburetor to allow more fuel to run to the engine, you must increase the level of air going into the engine. Likewise, if you change elevations by more than 1,000 feet you should adjust the amount of air going to your carburetor because the air is thinner.

Step 1

Turn on the motorcycle, drive it until the engine is warm and allow it to idle through the adjustment process.

Step 2

Locate the slotted screw on the left side of the carburetor, just above the bowl. The screw is basically the same on Keihin, CV and Mikuni carburetors commonly used on Harley-Davidson, Suzuki, Honda and Kawasaki motorcycles.

Turn the screw clockwise to decrease the amount of air going into the carburetor. The engine will reduce the RPMs (revolutions per minute). Turn the screw counterclockwise to add more air. The RPMs will increase. Adjust the carburetor until the engine idles between 1,500 and 1,1800 rpm or until the engine idles without stalling.

Items you will need

  • Flathead screwdriver

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