Small Engines (Lawn Mowers, etc.): LAWN TRACTOR, briggs stratton engine, briggs stratton

Question
I HAVE A CRAFTSMAN 20.5 HP LAWN TRACTOR WITH A BRIGGS & STRATTON ENGINE.MOD.# 917.270960 MY PROBLEM IS THAT IT WON'T START UNLESS I POUR GAS INTO THE CARB.
IT DID NOT HAVE THIS PROBLEM UNTIL I WORKED ON ANOTHER PROBLEM.THE ENGINE IS A TWIN CYLINDER, LAST WEEK IT STARTED RUNNING ON ONE CYLINDER,I CHECKED IT OUT AND DISCOVERED THAT THE KEEPERS CAME OFF ONE OF THE VALVES.I PUT THEM BACK ON, NOW I HAVE COMPRESSION FROM BOTH CYLINDERS,BUT IT WILL NOT DRAW THE GAS FROM THE TANK.THE FUEL FILTER IS NEW,I TOOK APART THE CARB.AND CLEANED IT,NO OBSTRUCTONS.ANY IDEAS? THANK YOU,ERIC  

Answer
Eric, You may have to revisit the fuel pump on the carb body. First detach the fuel line as see if fuel come out if OK re-attach. If you crank the engine..remove the UPPER HALF of the carb and see if gas is in there...and if there is no gas the pump may be bad......Bob