When you want to get more horsepower out of your lawn mower engine or if you want to turn it into a racing lawn mower, then you will need to take some specific steps to optimize your mower engine 's horsepower. The horsepower listed on your mower engine is not actually what the engine runs at as some restrictions hold back the horsepower; but there are also a few things that can get your mower running at its full horsepower.
Remove the flywheel housing from the top of your engine. Unscrew the bolts holding the housing over the top of the engine with the proper sized wrenches.
Unscrew the bolt holding the governor flap next to the flywheel with the proper sized wrench. When the lawn mower engine spins too fast, the governor flap blows out and slightly closes the carburetor, therefore decreasing the speed and horsepower of the engine. After unscrewing the governor flap, unhook the spring from the governor to the carburetor. Replace the flywheel housing on the engine.
Inspect the muffler. If the muffler is cracked or not properly sealed to the exhaust hole on the engine block, you will lose horsepower as the muffler produces back pressure to the engine. Check that the muffler is tightened to the engine block and the gasket is whole--there is a gasket between the muffler and the block. If the muffler is cracked, buy a new one and install it. They are fairly inexpensive and you only have to remove three or four bolts to install one.
Fill the gas tank on your mower with a high octane gas. Most operators use 87 octane gas as it is cheaper, but more expensive 92 octane burns quicker and increases engine power.
Maximize the air flow. High power engines need great air flow, so replace or clean the air filter on the engine every month.