1. Try taking out spark plug to see if it sparks, the spark is week so put your finger on it while pulling the cord slowly, if you feel it then that's that if not spray some carb and throttle cleaner down where the on off switch is to get a better connection to the body of the machine, I took mine apart to clean it with wire wool, make sure the plug is in good condition and the gap is correct, the coil is magnetised that generates the spark so could be worn out you can replace it easy enough.
That's the spark sorted now down to the fuel,
Petrol degrades when left for long periods so best to drain old fuel out of the machine and make sure the mixture is correct when adding fresh fuel.
The air filter can become blocked so take it out and clean with an airline or a Hoover then spray some carb/throttle cleaner down the opening its an awesome cleaner.
On first starting take out the spark plug crank the engine a few time to get the fuel going then warm the plug on the cooker or use a blow lamp this will help to ignite the fuel, you could even spray carb cleaner down into the air filter when cranking the engine,carburettors are sensitive to any alterations so if you have to replace parts then you may have to do some fine tuning, the carb cleaner will help in most cases, these engines are not fuel injected so every thing has to be perfect for them to run, last thing these engines have to have correct air/fuel mixture so check air adjustment screw is not to far in or out,
Hope that helps,
Chris, July 2016