Stihl is one of the world's leading retailers in chainsaws and has been making them for over 70 years. These chainsaws are rugged and often reliable. If properly maintained they will last for many years. But, like all chainsaws, they will break down at some point. Understand that chainsaws, like all two-cylinder engines, require only three basic things: compression, spark and fuel. If any of these components are misfiring or broken, your Stihl will likely run poorly or not at all.
Use the screwdriver to remove the cylinder cover. Take off the air filter and clean it with the gas, toothbrush and rag.
Take off the starter cover with the screwdriver. Inspect the cord, recoil spring and pulley for any damages and proper tension. Replace any parts, if necessary, and clean the starter housing area and fan with the toothbrush, a little gas and the rag. Put the starter cover back on.
Hold the saw by the starter cord. If the saw holds still, your compression is fine; if it pulls out the cord under its own weight the compression is low. Check the fan and clean inside the muffler.
Pull off the rubber spark plug boot and unscrew the spark plug with the socket wrench. Check the rubber plug, the boot attachment and the wires for any damage or loose connections. Replace these parts, if necessary.
Clean the spark plug with the gas, toothbrush and rag; make sure the tip isn't heavily corroded and is gapped properly. Check the owner's manual for spark plug gap recommendations.
Reattach the spark plug to the rubber plug, but leave it disconnected from the engine. Let the wire and plug dangle next to a metal spot on the engine.
Pull the starter cord and look across the points for a spark. If there's no spark, replace the spark plug and perform the test again. If there's still no spark, check the magneto gap, ignition coil and ignition module; replace if necessary.
Drain the gas and bar oil tanks of their contents. Wrap the rag around the toothbrush, spray a little carburettor cleaner into the tanks and clean them both thoroughly.
Use the needle-nose pliers to pull out and replace the fuel filter and fuel lines. Fill the saw with fresh gas at a 50:1 fuel-oil mixture.
Take off the cylinder cover again and spray starter fluid into the carburettor's opening, the little metal flap that opens and closes with the throttle. Try starting the saw.
Pull out the carburettor, disassemble it and clean every part by soaking them for two nights in a carburettor cleaner bath. After the bath, scrub them with a wire brush to make sure they're fully cleaned. Replace any worn parts or the entire carburettor if it's too old or dirty to be cleaned.
These tests are meant to serve as a basic framework to help isolate the problem into compression, spark or fuel.