Is the fuel primer bulb collapsed after it shut off? Check to see if this is happening. If it is 1 of 2 things is happening, The screen in the tank is clogged or the tank is collapsing on itself. The screen in the tank isnt so bad but if the tank is collapsed that calls for engine removal
raying:. How old is the machine? What year? Does the engine sit long ways in the frame or sideways? Does it smoke really heavy while idleing? How bout the air fliter, is it in good shape? Are you sure that theirs no air in the fuel lines? It could be just the primer bulb also.