The primer is a small rubber button that injects air into the carburetor that then forces some fuel through the carburetor jet into the intake. Manufacturers vary as to the number of pumps to the primer bulb suggested for starting the engine. The primer bulb can fail if the rubber breaks or the connection between the bulb and the carburetor becomes clogged or disconnected.
Things You'll Need
Wrenches and screwdriver
Replacement primer bulb
Repairing a Lawnmower Primer Bulb
Check the primer bulb to make sure it is working. The bulb should feel like it is pushing gas into the carburetor. If it does not feel like it is moving gas the fuel line from the tank to the bulb may be clogged or disconnected. It can also mean the bulb has deteriorated and does not create pressure when the bulb is pressed. Gas leaking from the bulb also indicated the rubber has cracked or broken.
Remove the primer bulb. Positioning of the primer bulb and the fastening methods used will vary from manufacturer to manufacturer. Check the operator's manual for possible instructions. The bulb will have two fuel line connections. One to the fuel tank and the other to the carburetor. The fuel line from the gas tank will need to be plugged after the bulb is removed to prevent leaks.
Check the primer bulb assembly. If the bulb is cracked or broken it should be evident once the bulb is removed. Clogs of the fuel lines from the tank to the bulb or from the bulb to the carburetor should also be noticeable once the bulb assembly is removed. If the fuel lines are clogged they can be cleared by forcing air through them or running a small wire through the opening. A broken or cracked rubber bulb will require replacement.
Reassemble the primer bulb and the lawn mower. Usually this is accomplished by following the same process as removing the bulb in the opposite order. Make sure the fuel lines are firmly attached to prevent gas leaks that could result in a fire on the lawnmower.
Start the lawn mower. Follow the manufacturer's instructions as to the number of pumps necessary to prime the engine. Do not over prime the engine. If the mower is still difficult, or impossible, to start the problem may be with other parts of the fuel system. Continue to trouble shoot the engine to determine the problem.