Husqvarna manufactures a wide variety of chain saws. The company has a reputation for making tough, reliable saws, but the saws are not indestructible. If the saw is running fine and you stop the saw for a moment and it will not restart, there are two systems that could be at fault. It's either the carburetion or the coil. Going through the troubleshooting procedure does require a knowledge of engine theory and will take 45 minutes to complete.
Place the Husqvarna chain saw on a hard level surface. Start the engine and let it run until it gets hot. Shut down engine and try to restart it. If it does not start, move forward with the diagnostic procedure. Pull off the small vent that is attached to the fuel line coming out of the gas tank. Pull the starting cord, if it starts, install a new vent. If it does not start, move to the next step.
Remove the air filter cover located on the side of the engine, just above the carburettor. Remove the air filter, exposing the carburettor. Spray a small amount of carburettor cleaner into the hole in the middle of the carburettor. Pull the starting cord. If the engine starts and then dies, the carburettor needs replacing.
Pull the fuel line off the side of the carburettor, remove the two screws holding the carburettor against the engine block. Twist the carburettor and slide off the throttle linkage. Install the new carburettor, slide on the throttle linkage, install the screws and push on the fuel line. If the engine did not start in Step 2, move to the next step.
Remove the spark plug wire from the spark plug. Plug one side of the spark tester into the spark plug wire and the other end to the spark plug. Pull the starter cord rapidly while watching the tester, if no spark is present, the coil needs replacing.
Remove the four hex screws that hold the plastic housing to the engine block. This will expose the coil. Remove the two hex bolts holding down the coil. Pull off the small black wire on the bottom of the coil. Install the new coil, hand tighten the hex bolts that hold the coil to the engine block. Make a small gap in between the flywheel magnets and the coil. A common business card can be used to create the gap. Tighten down the hex bolts with a wrench. Reinstall the small black wire and plastic housing.