With out the air cleaner on it, rev it up by hand. Then while it's at the higher rpm with your other hand hold a rag and stick it over the top of the carb. It will suck fuel from every port in the carb. When it slows down a bit pull the rag off. Clear it up and do it again a couple of times. The passages are full of spiders and varnish. It will come back to life it will just take time and driving.