Small engines are commonly used on lawn power tools such as lawn tractors, chain saws and snow blowers. Several things can cause an erratic performance in an engine's RPMs. To troubleshoot the problem, first check the RPMs in the idle speed and high idle speed positions. The procedure takes about 10 minutes.
Place the engine on a flat workbench.
Remove the spark plug wire from the spark plug located at the front of the engine. Remove the spark plug with the spark plug wrench, then inspect the spark plug. If the plug is dirty or fouled, replace it. Plug the spark plug wire back on to the spark plug.
Turn on the tachometer. Wrap the lead from the tachometer around the spark plug wire.
Start the engine, then move the throttle to the SLOW position. Take the reading from the tachometer. Refer to the specification page in the operator's manual for the correct operating range.
Move the throttle to the FAST position, then take the reading from the tachometer. Refer to the specification page in the operator's manual for the correct operating range.