Help! My riding mower is slow to crank after sitting idle for several days. It is a 5 year old Craftsman with a 17.5 hp Kohler engine and rear fuel tank. I crank it now by pouring a few drops of gas directly into the carburetor. It fires right up and runs very smoothly (no sputters, pops or stalls) the rest of way. The fuel line filter has been changed several times. I thought of trying to add a primer bulb onto the fuel line, but I can't find one. Any suggestions?