Many problems can cause your Stihl chainsaw to stop starting. These problems range widely in complexity and costliness. However, these two-stroke engines were designed to minimise the number of parts that can lead to engine failure. Determining the source of your problem will help you understand what it will take to get it fixed.
Ignition Spark Problems
The crankshaft in the Stihl engine powers a flywheel. When this flywheel spins, two magnets generate magnetic energy. When enough magnetic energy has been generated, the ignition module gets tripped. This sends the spark up to the plug where it ignites the fuel. Problems anywhere in the ignition system will stop your engine. Bad or corroded spark plugs, faulty wiring connections, broken wires, faulty ignition module or an improper air gap between the flywheel and the ignition module will all stop the engine from combusting. Start at the spark plug and work back to the ignition module and flywheel, checking all points on the ignition system.
Fuel Intake Problems
If a spark is being generated it needs enough fuel inside the cylinder at the right time. When the crankshaft spins, it creates a vacuum pressure on the carburettor, which sucks fuel up from the tank. The fuel is mixed with air in the carburettor before it's sent off to the cylinder. Anything that is restricting the flow of fuel or air will cause your mix to be off, which won't ignite in the cylinder. Dirty or clogged fuel tanks; dirty fuel filters and lines; loose fuel hoses; dirty air filters; and a dirty carburettor will all restrict fuel flow. Check, clean and replace all the fuel system parts before moving into the internal engine, as gas problems create a majority of starting problems.
The carburettor sucks fuel up from the tank, mixes it with air and then pushes it off into the cylinder. This system is regulated through three chambers: the metering section, where fuel is measured; the mixing section and the fuel pump. If this process can't work smoothly, the gas will cease to arrive in the cylinder with the right volume and at the right time. Dirty bores and jets, improperly seated needle valves, stuck levers and ripped or warped diaphragms will all stop the fuelling process. Remove, disassemble and clean the entire carburettor. Install a carburettor upgrade kit before replacing the carburettor.
Compression is necessary for the entire spark and fuel systems to continue work fluidly with one another. As the piston moves up and down in the cylinder, along with the crankcase, compression is generated. Compression can get compromised from an air leak somewhere inside the engine or from a clogged fuel or air system. When the compression isn't regulated properly the piston can seize up in the cylinder, effectively ending the engine's life. Compression problems need a professional mechanic.