How to Adjust the Air Mixture in a Carburetor

Updated February 21, 2017

The carburettor on a motorcycle has an air/fuel mixture screw to adjust the amount of air going to the engine. If you reset a carburettor 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 carburettor because the air is thinner.

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

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

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

Things You'll Need

  • Flathead screwdriver
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Since 2006 Zyon Silket has been writing for companies such as SEOWhat, L&C Freelancing and T-Mobile Wireless. He has extensive experience working in supervisory roles within the wireless and Internet technologies fields. Silket is pursuing a Bachelor of Arts in business management and network technologies at Lehigh Carbon Community College.