What is the reason of motorcycle idling instability?

The spring force of throttle return spring is poor or the lower edge of throttle is worn.

During maintenance, start the engine and adjust the carburetor idle speed adjusting screw, which is ineffective repeatedly. The acceleration test shows that the engine accelerates well and the exhaust smoke is normal. Check the throttle cable, and the valve clearance is normal. When the idle speed adjustment screw is removed, there will be idle speed. According to the above inspection, it can be preliminarily judged that the idle oil hole is blocked.