Gasoline-powered tools are driven by small engines that require a primer bulb. Whether it's a garden tool or a chain saw, a primer bulb helps small engines that lack carburetors start "cold" by advancing gasoline into the engine. Over time, a bulb can become weathered and rot or just wear out from use. As a result, primer bulbs may need to be replaced so the tools are available when necessary.
Make sure the engine is off. Put safety goggles on and place a funnel into a container to empty the gasoline from the engine. Place the engine containing the primer bulb on a drip pan, or onto a work area that can be easily cleaned if gasoline contacts it.
Inspect the engine and locate the primer bulb. It may be underneath the starter housing cover or connected to the fuel lines, which may be exposed along the edge of the engine. If it's under the starter housing, use a screwdriver to remove the housing screws and place the screws away from the work area so they won't be lost.
You may need an Allen wrench to remove the primer bulb from its mount. If so, remove the Allen screws and place them with the housing cover screws. Once removed, gently pull the old primer bulb from the fuel lines. Examine the fuel lines to make sure they're in proper working condition without any cracks or weathered appearance.
Inspect the new primer bulb and note the ribbed ends. Hold the new primer bulb up to the fuel lines to measure for a proper fit. If necessary, use scissors to cut the ends of excess fuel line to adjust for any difference in size. Push the new primer bulb onto the fuel lines while making sure to connect the fuel lines securely over the ribbed ends. Reposition it back onto the mount by fastening it to the engine with an Allen wrench and screws. Replace the housing cover, then tighten the screws with a screwdriver. Refill the tank with the gasoline drained at the beginning of the procedure.