I have a 7 hp Briggs stratton , huffy sheraton ,riding lawn mower,when you turn the gas on from the tank to the carb , it will not start .but when you cut it off, it will run till the gas in the bowl runs out what do I do? What is wrong please help if you can if any body can help

It sounds like the vent in the carburaetor may be plugged. Not allowing fuel into the carb.Pull the carb apart and clean it thoroughly. There is a small vent hole on the side of the carb facing to the outside of the engine. Make sure that is clean.

Try loosening the gas cap and try running it. The vent holes in the cap may be plugged.

Or, you could have a float and needle problem.