Try removing the brass nut on the bottom of the carb and carefully drop the bowl. Shut the fuel valve under the tank first. You may have a bit of crud that occasionally gets into the jet. Be careful that the inlet seat does not drop out of the bore and the bowl gasket is properly seated when you reassemble it.

You mentioned "Steep" driveway, Sometimes if the driveway is steep, you can stal out, I had that haoppen to a Customer. But like what was mentioned, Clean the carb and see if that helps. Patrick