How to Adjust the Idle Screws on a Carburetor

by Chris Gilliland
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Your motorcycle relies on a proper mixture of air and fuel to power its motor. This mixture is governed by the carburetor, which pulls air into a channel called a venturi and mixes with gas before entering into the motor. At a standstill, the air must pass through a small opening between the throttle valve and the venturi, letting a small amount of the mixture into the motor and allowing the motorcycle to idle. At idle, the throttle valve is controlled by the carburetor's idle screw, increasing or lowering idle speed by opening or closing the valve.

Step 1

Place your motorcycle in neutral and start the motor. Let the motor run for a few minutes to warm up. Once warm, take note of the motorcycle's engine idle speed. Most motorcycles require an idle speed of 1,100 to 1,300 RPM (revolutions per minute) to operate properly at a standstill.

Step 2

Turn the idle screw slowly using a screwdriver, twisting the screw counter-clockwise to lower the motor's RPM or clockwise to increase RPM. Stop adjusting the screw when the tachometer indicates the desired RPM range.

Step 3

Twist the throttle open a few times and observe the tachometer needle as the RPMs fade. The needle should return to the desired idle speed. If not, readjust the idle and test it again.

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