1.Throttle stuck open. Spray carburetor cleaner in the air horn to break up varnish, which may be holding the throttle plate open. If this does not do it, then spray WD-40 in the air horn and see if this frees it up. Also spray WD-40 on the throttle shaft on the outside of the carburetor.
2.Govenor is incorectly adjusted or not working at all.To staticly adjust the governor, locate the governor arm and loosen the nut on the bottom of the arm. Rotate the governor arm so the throttle is in the wide open position. Now hold what you got and turn the governor shaft in the same direction you rotated the arm. Tighten the nut and that will do it. If you are adjusting a Tecumseh governor, loosen the screw with a 1/4" nut driver and follow the above procedure.
If the govenor is not functioning at all, then chances are it has fell apart in the engine for various reasons (mechnical govenors only). This must be replaced or your engine will run at excessive speeds and may cause internal failure of the engine.
3.Govenor linkage is improperly connected to the carburetor. If this is the case, then E-mail me and I will send you instructions on hooking up the govenor linkage. Click Here If you need diagrams for Briggs and Stratton engines. Click Here If you need a diagram for Tecumseh engines.