Chainsaw Repair

Or you can crack the fuel cap open alittle to let air into the tank to see if it stays running or dies.   If it stays running then you know the vent is plugged up.

Could be a bad fuel filter.   Checked fuel line and make sure it is not showing any cracking any where.   

When it dies pull the plug attach it to the plug wire and hold it against the top of the cylinder and verify you have spark.

There are other possibilities but this is a good place to start.