If your motorcycle is not starting despite having addressed common issues like carbs, electrical problems, spark plugs, and valve adjustments, there could be a few other potential reasons for the starting trouble. Consider the following possibilities:
Fuel-related issues: Check if there is fuel in the tank and that it is reaching the engine properly. Verify that the fuel lines are not clogged or damaged, and that the fuel filter is clean. If your motorcycle has a fuel pump, ensure it is functioning correctly.
Ignition system problems: Although you mentioned electrical issues as not being the cause, it's still worth examining other components of the ignition system. Inspect the ignition coils, ignition switch, and wiring connections to ensure there are no loose or damaged connections.
Compression issues: Low compression can lead to starting problems. If you recently performed a valve adjustment, double-check that it was done correctly. Incorrect valve clearances can affect compression. Additionally, if your motorcycle has a compression release mechanism, make sure it is functioning properly.
Timing issues: Verify that the ignition timing is set correctly. Incorrect timing can prevent the engine from firing up. Consult your motorcycle's manual for the recommended timing specifications and adjust if necessary.
Air intake and exhaust restrictions: Check if there are any obstructions in the air intake system, such as a blocked air filter or a clogged airbox. Similarly, ensure the exhaust system is not restricted or blocked.
Mechanical problems: Certain mechanical issues can prevent the engine from starting. Examples include a faulty starter motor, a seized engine, or damaged internal engine components. If you suspect a mechanical problem, it may be best to consult a professional motorcycle mechanic for a thorough inspection.
Remember to take appropriate safety precautions when working on your motorcycle, such as wearing protective gear and following proper maintenance procedures. If you are unsure about any aspect of troubleshooting or repairing your motorcycle, it is always recommended to seek assistance from a qualified mechanic.