If your dirt bike's engine RPMs remain high after releasing the throttle while it's in neutral, it could be due to a few potential causes:
Sticky or improperly adjusted throttle: A sticky throttle cable or throttle tube can prevent it from returning to its idle position smoothly. This can keep the throttle partially open, resulting in higher RPMs. Adjusting or lubricating the throttle components may resolve the issue.
Air intake or vacuum leak: An air leak in the intake system, such as a cracked or disconnected hose, can cause the engine to draw in extra air, leading to a higher idle. Inspect the intake system for any leaks and ensure all connections are secure.
Idle adjustment: The idle speed screw or idle air/fuel mixture may need adjustment. If they are set too high, it can cause the engine to idle at a higher RPM. Consult your dirt bike's manual or a mechanic to properly adjust the idle settings.
Carburetor issues: If your dirt bike has a carburetor, it may be dirty, clogged, or require adjustment. A dirty carburetor can disrupt the fuel-air mixture and affect the idle speed. Cleaning or tuning the carburetor might be necessary.
Throttle position sensor (TPS) malfunction: Some modern dirt bikes have electronic throttle systems with a TPS that communicates with the engine control unit (ECU). If the TPS is faulty or not properly calibrated, it may cause the engine to maintain high RPMs. A diagnostic scan or inspection by a mechanic can identify TPS-related issues.
Ignition system problems: Faulty spark plugs, ignition coils, or other ignition components can cause irregular engine operation, including high idle. Inspecting and servicing the ignition system may be necessary.
If you're unsure about diagnosing or fixing the issue, it's recommended to consult a qualified mechanic or technician who can inspect your dirt bike and provide accurate diagnosis and repairs.