While Tecumseh builds a variety of small engines for use in lawn and garden equipment, the 8HP Tecumseh engine is most popular on small riding lawnmowers and other larger lawn equipment. The 8HP Tecumseh engine uses a carburettor to provide the proper mixture of gasoline and air to the engine. If the engine is running roughly, adjustments to the carburettor can often smooth out both the idling of the engine and when the engine is running at full throttle.
Locate the main mixture adjustment screw. On float-style carburettors, this screw is located underneath the float bowl on the bottom of the carburettor. On diaphragm carburettors, there are two screws on one side of the carburettor, and the main mixture screw will be the one on the right.
Finger-tighten the main mixture screw. Do not overtighten.
Insert a flathead screwdriver into the main mixture screw. Rotate the screw counterclockwise one full turn for diaphragm carburettors, and one-and-a-half turns for float-style carburettors.
Locate the idle mixture adjustment screw. On diaphragm carburettors, this is the adjustment screw to the left of the main mixture screw, while on float-style carburettors it will be the only adjustment screw on the side of the carburettor.
Finger-tighten the idle adjustment screw. Do not overtighten the screw.
Insert a flathead screwdriver into the idle adjustment screw and rotate counterclockwise one full turn for both types of carburettors.
Start the engine and set it to idle. Adjust the idle adjustment screw in small increments until the engine idles smoothly.
Open the engine up to full throttle and adjust the main mixture screw until the engine runs cleanly and at full power.
When adjusting the two screws with the engine running, you may need to turn clockwise or counterclockwise to remove or add gasoline from the mixture. Listen for smoothness in the running of the engine and adjust the screws accordingly.
When adjusting your running engine, do not engage the engine with the transmission, blade or other working implement.