If a carbureted motorcycle engine is receiving spark but still fails to start, even when using starter fluid, there could be several potential issues at play. Here are a few possibilities to consider:
Fuel delivery issues: While you mentioned using starter fluid, which provides an external source of fuel, it's possible that the carburetor is not delivering the necessary fuel to the engine. This could be due to a clogged fuel line, a malfunctioning fuel pump (if applicable), a stuck float in the carburetor, or a blocked jet. Inspecting and cleaning the carburetor components, including the jets and float bowl, may be necessary.
Ignition timing: Even though the engine is receiving spark, the ignition timing could be off. If the timing is not properly synchronized with the engine's cycle, it can prevent combustion from occurring at the right moment. Checking and adjusting the ignition timing according to the manufacturer's specifications could help resolve the issue.
Compression problems: A lack of sufficient compression in the engine's cylinders can hinder starting. This could be caused by worn piston rings, damaged cylinder walls, or a leaking head gasket. Conducting a compression test to measure the compression levels in each cylinder can help identify if this is the problem.
Air intake issues: If the engine is not receiving the necessary amount of air, it can impede starting. Check for any obstructions in the air intake system, such as a clogged air filter or a blocked intake manifold.
Electrical problems: While you mentioned that the engine is getting spark, it's still worth inspecting the electrical system for any potential issues. Check the condition of the spark plugs, ignition coils, and wiring connections. Ensure that the battery has sufficient charge and that the starter motor is operating correctly.
It is recommended to consult a qualified mechanic or motorcycle technician to diagnose and resolve the specific problem with your motorcycle engine. They have the expertise and tools to perform thorough inspections and repairs to get your motorcycle running properly again.