If a motorcycle has spark and fuel but still won't start, there are several potential causes to investigate. Here are some troubleshooting steps you can take:
Check the Battery: Ensure that the battery is fully charged and in good condition. Weak or discharged batteries can prevent the motorcycle from starting. If necessary, charge or replace the battery.
Verify Fuel Flow: Even though you have fuel, confirm that it is reaching the engine properly. Check the fuel lines, fuel filter, and carburetor (or fuel injectors) for any clogs or blockages. Ensure that the fuel is flowing freely to the engine.
Assess Air Intake: Make sure the air filter is clean and not clogged. A dirty or blocked air filter can restrict airflow, affecting combustion and preventing the motorcycle from starting. Clean or replace the air filter as needed.
Inspect Ignition System: Check the ignition system components, including spark plugs, ignition coils, and wires. Ensure the spark plugs are in good condition and properly gapped. Faulty ignition components can cause weak or intermittent sparks, leading to starting issues. Replace any faulty parts if necessary.
Examine Carburetor/Fuel Injectors: If your motorcycle has a carburetor, it may require cleaning or adjustment. Carburetors can get clogged over time, leading to starting problems. If your motorcycle has fuel injectors, consider having them professionally cleaned. Improper fuel mixture or injector issues can affect starting.
Check Engine Compression: Low engine compression can make it difficult for a motorcycle to start. Use a compression tester to check the compression levels in each cylinder. If the compression is low, it may indicate worn piston rings or cylinder head issues, requiring further inspection and repair.
Electrical Connections: Inspect all electrical connections, including wiring harnesses, switches, and relays. Loose or corroded connections can disrupt the electrical flow and prevent proper starting. Clean or tighten any loose connections.
Consider Other Factors: If none of the above steps resolve the issue, there could be other factors contributing to the starting problem. These may include a faulty ignition switch, malfunctioning safety switches (sidestand switch, clutch switch), or an immobilizer system (if equipped). Consult a professional mechanic or refer to the motorcycle's service manual for further diagnosis.
If you're not confident in your mechanical abilities or unable to diagnose the issue, it's recommended to seek assistance from a qualified motorcycle mechanic. They have the expertise and specialized tools to diagnose and fix complex starting problems.