Briggs & Stratton engines are used in lawnmowers, snowblowers, rototillers, log splitters and many other lawn and garden implements. These engines have a governor that is designed to increase the engine speed when the machine is under a heavy load, or lower the engine speed when the load is limited (to keep the engine from over-revving). If the engine is running roughly, a repair to the governor on a Briggs & Stratton engine may solve the problem.
Disconnect the spark plug wire from the spark plug by pulling on the black rubber boot covering the tip of the spark plug.
Inspect the linkage between the governor arm on the side of the engine and the carburettor. If the spring is stretched excessively, or the linkage is damaged, replace with genuine Briggs & Stratton linkage parts before continuing with the following steps.
Push the governor arm to the left and then to the right. The governor arm should move easily, opening and closing the throttle as you move the arm.
Loosen (but do not remove) the nut at the base of the governor arm with a wrench or socket so that the arm moves freely.
Push the throttle linkage into the open (full speed) position, and notice which way the governor arm moves as you open the throttle. Push the governor arm in this same direction with your hand as far as it will go, then tighten the nut at the base of the governor arm.
Release the throttle control, and manually move the governor arm (as you did earlier in Step 3), to make sure the linkage still moves the throttle properly.
Reconnect the spark plug wire to the spark plug, and start the engine. Let it warm up a couple of minutes, then put the engine under a workload, to see if the engine continues to run smoothly. If the governor is set properly, the engine should run smoothly when under a heavy workload or no workload.