Pull the cord to determine if there is play or not. If the cord does not move, the problem is where the cord meets the pulley wheel. If the cord does pull but pulls slowly, the problem may be the blade. Lift the front of the mower to determine if the blade is caught or jammed. If the cord pulls but is loose and fails to turn the pulley wheel, the problem is the cord. If the cord pulls but does not retract, the pulley wheel is jammed, or the cord has snapped.
Remove the screws that hold the top of the engine housing in place. There are either four screws, one at each corner, or a single screw in the middle. Lift the housing off to gain access to the pulley wheel. Pull the wheel straight up and out of the housing, along with the cord. Look for any debris caught between the cord and the wheel. Inspect for cracks, nicks or sharp edges on the wheel. Look for fraying or breaks in the cord. If nothing is apparent there, lift the mower and check the blade and shaft. If either the blade or shaft is bent, this could prevent the pull cord from working because the pulley wheel is connected to the top end of the shaft. Remove any debris or obstructions, reassemble the mower and try starting it again.
Cords that have frays, breaks or signs of wear should be replaced. Unwind the cord and cut off the end at the wheel. Measure the length between the top of the mower handle to the motor and double that to accurately determine the length of the new cord. Thread the new cord through the hole in the wheel and tie a knot on the inside of the wheel. Rewind the cord entirely then reassemble the cord and wheel onto the mower. Pulley wheels with bends, fractures or sharp edges should be replaced immediately. A bend in the wheel indicates warping due to heat or friction, and the wheel will eventually break at that point. Fractures indicate weak points in the wheel, and sharp edges denote already broken sections that can widen, causing the wheel to snap into pieces. The mower blade and shaft can become bent or fractured from obstructions, rust or striking another object. When damaged sufficiently, either the blade or shaft can cause the mower not to function. If the blade is damaged, unscrew the center bolt that holds the blade and replace it. If the shaft is damaged, you may need a professional repair service to replace it; shaft repair requires disassembly and removal of the motor and parts associated with it, including the pulley wheel.
Avoid mowing grass or weeds higher than the mower. Plants can get caught in the housing. Plants with sharp edges, thorns or rough areas can cause damage to the cord and blade when they get entangled. Avoid rough surfaces and rocky terrain. Dirt, debris and rocks can be driven into the blade, shaft or motor housing, causing damage to parts used to start the mower.