There are a few basic maintenance things common to most small engine that would be a good start.
Replace the fuel filter and use fresh fuel
Replace the spark plug
Clean/replace air filter
If it is old and has them, check the points and points assembly, if readily available, just replace the points and condensor
If it has sat along time with gas in it, the carb will need dissassmbly and cleaning. This isn't very hard, just do it in a well lit and clean area so anything you drop will be found. Use some carb cleaner and whatever else you need to wash the chunks of stuff away. Check if the flaps for the pump are in ok condition.
I would take a guess at the fuel filter or air filter. The fuel filter is weighted in the fuel tank. To get it out, drain the gas out and tip the saw or use a wire to fish it out. Sometimes more line will have to be fed into the tank (the hose passes through the tank from the carb) to allow you to hold the hose to push the new filter on.
Hope this helps.
Ken
