Mower starts and runs only when tipped up

i have a craftsman 917.376572 that has a Briggs and Straton engine. the mower will start every time i pull the cord but will only stay running if the handle is pushed nearly to the ground. if i level it out (to normal mowing position) it dies almost immediately. i have checked the gas tank and line and made sure the float in the carburetor isnt sunk and is free. i really dont want to have to buy a whole new mower when this one does run.



additional info: recently the engine was abruptly stopped by a curb but it started right back up then and was able to finish mowing the yard. only a week later when i went to use it again did it start showing this particular problem.



thanks