When you use a gasoline engine, you maybe encounter the following problems, failed to start, insufficient power, unstable working and engine sudden stall when working. Generally, you can check three parts: 

1.ignition system 

magneto coil, CDI, and spark plug. 

2.fuel supply system

gas tank switch, gas line, carburetor, and fuel filter. 

3.the engine block

the wear of cylinder, crankcase, piston, piston ring, bearing, oil seal, crankshaft, etc. 

Or the wear and destroy of clutch parts.

When a gasoline engine breaks down, you should carefully analyze and find out the causes, and timely eliminate it. If you are not sure for the cause, you can check the engine system one by one.