Incorrect idling can drastically affect a motorcycle's performance. Low idle speeds can cause the bike to shudder when standing still and make stalling more likely, while a high idle speed makes riding slowly difficult. The idle on a motorcycle will likely require adjustment after any maintenance on the throttle cable, but a number of more serious problems can manifest themselves as an idling problem. These issues include improper valve alignment, defective ignition system, worn spark plugs and clogged carburettors. Be aware of such potential problems, as primitively adjusting the idle speed will only mask them.
Start the motorcycle, and allow the engine temperature to reach normal operating levels. The time the engine will take to reach the desired temperature depends on the ambient air temperature but will generally range from five to 10 minutes.
Look in the owner's manual for your motorcycle under the section titled "Periodic Maintenance," and find the specified engine idle speed. The recommended speed varies for different countries and year of manufacture but will generally be about 1,200 revolutions per minute (rpm).
Locate the throttle stop screw, a small black knob about 1cm in diameter, situated on the left side of the motorcycle,just below the tank beside the carburettor.
Turn the throttle stop screw clockwise to increase the idle speed, and turn it counterclockwise to decrease the speed. Perform this step until the rev counter shows the correct idle speed.
Rev the engine gently with the throttle, and ensure that it does so smoothly and quickly slows to idle speed again. If the engine is not responsive (that is, if it lingers just above idle speed for a couple of seconds before settling), reduce the idle by half a turn on the throttle stop screw.
Turn the handlebars from side to side, and check that this action doesn't increase the engine idle speed. If so, the throttle cable may be too tight and require adjustment.
- If the throttle stop screw will not adjust the engine idle speed sufficiently, you may have a more serious problem. Seek assistance from a registered dealer, who will be able to diagnose the problem.