atco balmoral won't start?

My Atco Balmoral 20 won't start after the winter. I've put new petrol in, pulled the recoil 20 - 30 times and no success. I've checked the plug. The gap is correct and the plug hardly any wear. But it wasn't wet, so I think no petrol getting through. Guess its blocked somewhere. Are then any filters that can get gummed over winter or the carburetor itself.
Any ideas where to start please.