Many people are interested in making their riding lawn mower go faster for racing purposes or just to get their lawn mowed faster. Riding lawn mower engines have a governor to prevent them from going too fast, but you can remove this. You can also check out a few more things on your riding mower engine to ensure it is optimized for top speed and horsepower.
Remove the housing bolted over the flywheel. Use the proper size wrenches to unscrew the bolts around the perimeter on the housing.
Unscrew the bolt at the end of the governor (a white plastic flap) on the magneto next to the flywheel. Remove the nut from the side of the white plastic flap and remove the governor. Reinstall the nut. Unhook the springs connecting the governor to the carburetor linkage.
Bolt the housing back over the flywheel.
Analyze the muffler to ensure that it is sealed to the exhaust hole. If there is any gap or improper seal between the muffler, gasket and exhaust port, the engine will lose back pressure and decrease in horsepower.
Unscrew the air filter cover on the top of the riding mower engine with the proper size wrench (or screwdriver). Replace the air filter so the engine can get maximum airflow with a clean filter.
Add a high octane gas (92 octane) to the gas tank on the riding lawn mower. High octane gas is more expensive but it burns faster to provide more power to the engine.