Re: Engine quit running
Wow, this is an old post - 2003. Since I have a Force 120 and had the engine stalling problem myself I thought I would put in my 2 cents anyway.
Things to check:
Assuming you are not out of fuel is the vent on the fuel tank cap open? It should be open. Will squeezing the primer bulb get the motor started again? If so, it is likely that your fuel pump needs to be rebuilt.
Visually follow the fuel line to a small square box on the side of the cylinder head. There should be three tubes connected. Fuel in, fuel out, and vacuum. The box is attached to the side of the cylinder block with two screws. The other two screws hold the fuel pump together.
The fuel pump consists of 3 metal sections separated by two neoprene diaphragms and cardboard gaskets. My diaphragms were all puckered up and wrinkled. I think the previous owner ran carburetor cleaner through the system and damaged the diaphragms. The interior of my fuel pump was clean as a whistle but the diaphragms were shot.
Carefully observe the orientation of the diaphragms and the gaskets. The diaphragms look identical but the gaskets are different. Since this fuel pump is symetrically square, there are a dozen wrong ways to put it together but only 1 right way. Hint: observe the triangle shapes on one edge of each gasket and match them up with similar shapes on the pump housing.
Under the diaphragms there are a couple of spring loaded plungers and check valves. Take your time with a clean work area and you should be able to do this just fine. When reinstalling the fuel pump be sure to replace the long narrow cardboard gasket with three holes that goes between the pump and the motor. If you reinstall the rebuilt pump and the engine won't run for more than a few seconds you made a mistake in the assembly. Take it all apart and carefully compare your work to the photos in the Clymer's manual or similar publication.
How it works: The pulsating vacuum from the crankcase pulls the diaphragms in one direction. The spring loaded plungers push the diaphragms back in the other direction. The check valves keep the fuel flowing in one direction only.
