Maintenance issues with small engines come up all the time. These issues can be fixed by the knowledgeable owner/operator that would like to save money that would otherwise be spent on service dealer fees and parts that may or may not need to be replaced. Small engine adjustments can be made to help the engine run better, idle smoother and help increase fuel economy. If the engine idles at a speed that is higher than is recommended, gasoline is being wasted while the engine idles. Keeping the exhaust and the fuel system in tip-top shape will help prevent future problems.
Remove the air filter cover. Turn the idle screw counter-clockwise with a screwdriver if the engine idles too high. You will be able to tell that the engine idles too high because the pitch of the engine will be high. The tines may also turn while the engine idles. This is not normal, or safe for the operator, and should be corrected. The idle screw is located under the carburetor below the H and L screws. The engine should be running while the adjustment is made so you know when the idle speed is decreased sufficiently.
Adjust the carburetor and the idle screws if the engine runs rough. If the idle screw has already been adjusted and the engine still runs (not idles) rough, the carburetor screws need to be adjusted. The carburetor has a red, high-speed screw and a white, low-speed screw. Remove the tines, start the engine and open and close the choke a few times to eliminate any air from the fuel system. Turn the engine off when the engine reaches the normal operating temperature. Turn the red screw counter-clockwise until it stops. Set the white screw so it is between "counter-clockwise stop" and "clockwise stop". Restart the engine and run it at full speed for a few seconds and return the engine speed to idle. Accelerate to full throttle multiple times to see how the engine transitions from high speed to idle. If the engine hesitates, turn the white screw counter-clockwise one-eighth of a turn per attempt until the transition becomes smooth. Reinstall the tines.
Remove the spark plug to begin the process of cleaning the muffler screen. A dirty, clogged muffler screen can choke the engine and inhibit the exhaust from exiting the cylinder.
Remove the red cover which is held in place with two Phillips screws and one hex screw. Remove the exhaust guide (three more Phillips screws). The screen sits behind the exhaust guide and the muffler gasket. Inspect the condition of the screen. If there are black carbon deposits attached to the screen, use carburetor cleaner to remove the deposits. Use a soft metal brush to work the deposits loose. If the deposits do not come off of the screen, it should be replaced.
Reassemble each part in the reverse order that it was removed.