1. Fuel mixture: If the fuel mixture is too rich, the engine will run hotter and produce more unburned fuel, which can lead to flames coming out of the tailpipe. To check the fuel mixture, you can use a spark plug reader to see if the plugs are black or sooty. If they are, the mixture is too rich. You can adjust the fuel mixture by turning the carburetor's air/fuel mixture screw.
2. Spark timing: If the spark timing is too retarded, the fuel will not have enough time to burn completely before the exhaust valve opens, which can also lead to flames coming out of the tailpipe. To check the spark timing, you can use a timing light to see when the spark plugs are firing. The spark should occur just before the piston reaches the top of the cylinder. You can adjust the spark timing by turning the distributor or camshaft.
3. Exhaust system: If the exhaust system is restricted or blocked, it can cause the engine to run hotter and produce more unburned fuel, which can lead to flames coming out of the tailpipe. To check the exhaust system, you can remove the muffler and take a look inside. If there is a lot of carbon buildup or other debris, it may need to be cleaned or replaced.
4. Other problems: If the fuel mixture, spark timing, and exhaust system are all in good working order, there may be another problem causing the flames. Check the fuel injector, spark plugs, and any other components that might be malfunctioning.
If you are unable to fix the problem yourself, take your motorcycle to a qualified mechanic.
