Clean the air filter and check the float valve isn't clogged with crap.
It's the little knurled hand screw located on the carb, held in place with a spring. Unscrew it fully and remove. There will be a spike on the end of it. When you have taken it out fuel should leak out, give it a wipe and replace. This will also adjust the tick over which will alter depending on the engine temp.
If this has no effect, then check the all the fuel hoses for splits. If still no joy then look at the electrics, spark plug etc.......