If your motorcycle engine turns off after just a few seconds from idle, even after adjusting the carburetor RPM, there could be a few potential causes for this issue. Here are a few things to check:
Idle speed adjustment: Double-check that you have adjusted the idle speed properly. If the idle speed is set too low, the engine may struggle to maintain idle and stall. Consult your motorcycle's manual for the correct idle speed specifications and make sure it is set accordingly.
Fuel delivery issues: Inspect the fuel system for any clogs or obstructions that could impede proper fuel flow. Check the fuel filter, fuel lines, and ensure that the carburetor is clean and free from any debris. If necessary, clean or replace the fuel filter and clean the carburetor.
Air intake issues: Make sure the air intake system is clean and free from blockages. Check the air filter and ensure it is clean and properly seated. A clogged or dirty air filter can restrict airflow and affect engine performance.
Vacuum leaks: Check for any vacuum leaks in the intake manifold or carburetor. Vacuum leaks can disrupt the air-fuel mixture and cause stalling. Inspect the intake manifold gaskets and carburetor seals for any signs of cracks or leaks. Replace any damaged gaskets or seals as needed.
Carburetor adjustment: While you mentioned adjusting the carburetor RPM, there are other settings that could be affecting the engine's performance. The pilot jet and mixture screw settings, for example, play a crucial role in idle stability. Consider consulting a motorcycle mechanic or a knowledgeable person to ensure all carburetor settings are properly adjusted.
If you have performed these checks and the issue persists, it is advisable to seek the assistance of a qualified motorcycle mechanic who can diagnose the specific problem and provide a solution. They will have the expertise and necessary tools to troubleshoot and rectify the issue effectively.