The primer bulb on a McCullock 3216 chainsaw draws fuel from the tank into the carburettor when you depress it. When you release the primer bulb, the excess fuel goes back into the tank. This bulb helps with cold starts by allowing enough fuel to saturate the carburettor. When this rubber bulb cracks or has lost its suction with the carburettor, it won't properly draw gas through the line and you will need to replace it.
Unscrew the top cylinder cover's two screws with the screwdriver. Pull the cover off. Unscrew the top screw holding the cover onto the top of the air filter box. Remove the air filter cover and air filter. Unscrew the two screws holding the air filter box to the engine. Remove the air filter box.
Unscrew the top recoil assembly cover's four screws with the screwdriver. Remove the recoil assembly's cover and the recoil assembly with it. Unscrew the seven screws holding the starter cover and half of the handle over the starter. Pry this cover off and the primer bulb will come with it.
Grab and pull the old primer bulb off the starter cover with the needle-nosed pliers. Fit the new primer bulb into the hole and twist it down tight. Set the starter cover back in place. Fit the end of the primer bulb back onto the return fuel line.
Screw the starter cover's seven screws back in place. Set the recoil assembly over the flywheel and tighten its four screws to secure it in place. Set the air filter box back into place. Tighten both of its screws. Set the air filter into the box. Set the cover back on top and tighten the screw. Place the cylinder cover back over the engine and tighten both of its screws.