Walk-Behind Lawn Mower: Can't pull the starter rope
If the starter rope won't budge when you pull it, first check under the mower for a stick or other object blocking the blade—the motor won't spin if the blade is blocked. If the blade moves freely, pull off the recoil starter and pull the starter rope. If you still can’t pull it, replace the recoil starter. If you can pull it with the recoil starter removed, the problem could be a locked-up engine; have a service technician examine and repair the engine.
Troubleshooting video: Lawn Mower Won’t Start: Can’t Pull Recoil Starter Rope.
These repairs may help solve your Walk-Behind Lawn Mower problem:
Replace a lawn mower recoil starter assembly
The recoil starter on top of the engine has a spring that retracts the starter rope used to pull-start a gas mower. If the rope doesn't retract after you pull it, it's likely the spring is broken. Replacing the spring itself is difficult and dangerous, so the best way to repair a recoil starter is to replace the whole recoil starter assembly.
Replace a lawn mower starter rope
The starter rope is a heavy nylon cord that coils around the pulley and spins the recoil starter when you pull the rope. When the rope breaks, you can't spin the recoil starter to start the engine. Replace the starter rope if it's broken.