I recently obtained a briggs and stratton 20hp riding mower that won't run. Free of course. The original owner said it quit running one day while cutting the yard. I took the carb apart and cleaned it. It was reinstalled and an attempt was made to crank it. When it did not crank, I squirted gas in the carb and it started but went dead. It will run as long as gas is squirted in the carb. The fuel line is clear to the fuel pump at the front of the carb. The fuel pump is square with 4 screws holding it to the carb. After running the engine a few minutes by the squirt method, I pulled the top of the carb off and found no fuel in the bowl. I put a different carb from another mower on it and got the same results, it will only run if gas is introduced in the carb. I believe I have narrowed the problem down to what ever makes the fuel pump work. Is the fuel pump operated by vacuum? What creates the vacuum? That may be my problem. There is 5/16 hose that runs from the rh side of the fuel pump to the block. Is this a vacuum hose that operates the fuel pump?