DIAGNOSIS Insufficient power delivery or excessive load. Check three items: cutting height, extension cord, and deck clearance.
FIX Step one: Set the cutting height to a higher setting. Do not cut more than one-third of the grass blade height at once. Step two: Verify you are using a 14-gauge (or heavier), 50-foot maximum extension cord. A lighter cord starves the motor. Step three: Ensure the deck is clean (see cleaning procedure). A clogged deck creates drag.
IF THAT DIDN'T WORK The carbon brushes in the motor may be worn. The MJ401E uses replaceable carbon brushes. Access requires disassembling the motor housing.
HEADS UP This is a 13-amp motor in a 14-inch deck. It has power for its size, but you must mow at a steady, deliberate pace, especially in thicker growth.