I'd bet money that you have tiny grass clippings, dirt & misc. crud in the bowl of your carb.
If you're comfortable doing something like this, here's what I'd suggest...
1. Find the gas line & clamp it (small vice-grips, etc.).
2. Remove the bolt from the bottom of the carburettor bowl. It's probably a 7/16" head.
3. Carefully remove the bowl, making sure you pay attention to the gasket.
The bowl should have some gas in it. Mostly likely, you'll find quite a bit of crud in there. Clean it out and re-install it, making sure that it's turned in such a way that the indentation in the bottom of the bowl is lined up so that the float can lower properly. Be careful to make sure the o-ring/gasket is properly in place.