How to Adjust the Idle Speed of a Underbone Motorcycle?
2 Answers
Tighten the idle adjustment bolt, then loosen it by 1.5-2.0 turns. Slowly loosen the throttle bolt to reduce the engine speed to a very low level, almost to the point of stalling. Adjust the bolt to raise the engine speed to its highest point. Repeat this process 2-3 times until adjusting the idle bolt no longer increases the engine speed. The engine speed should reach the required range (800-1000 RPM). Accelerate and then release the throttle to check if the engine stalls. If it doesn't stall, it means the idle speed has been properly adjusted.
Adjusting the idle speed of a pit bike isn't actually difficult, and I often do it myself. First, you need to warm up the bike—let the engine run for a few minutes until it reaches normal operating temperature. Otherwise, cold adjustments can be inaccurate and prone to errors. Find a quiet spot and prepare a small screwdriver. The idle adjustment screw is usually located near the carburetor and is darker in color. Turn it slowly, don’t rush, and listen for changes in the engine sound as you adjust. The target RPM should be around 1,000 to 1,500—too high and it’ll be noisy and fuel-consuming, too low and it may stall or run unevenly. My experience is to test-ride after each adjustment; if acceleration is smooth, you’re good. Also, check if the air filter and spark plug are clean, as these affect idle precision. Once, my idle kept fluctuating, and it turned out the air filter was clogged. Regular maintenance reduces such issues. Safety tip: Wear gloves, avoid crowded areas, and be cautious of hot engine parts. If your bike has fuel injection, the steps are similar but may be more intuitive—check the manual. With patience, you’ll get it right.
