If an outboard primer bulb fills with fuel but does not get firm, there is likely a leak in the system on the engine side of the bulb. A primer bulb not filled with fuel and not firm indicates an empty fuel tank or blockage upstream of the bulb.
Primer bulbs are used to manually pull fuel from the tank to the outboard engine before a cold start. Once running, the mechanical fuel pump in the engine pulls fuel directly from the tank. In a properly functioning system, the empty bulb fills with fuel after several squeezes, becoming too firm to squeeze once the complete fuel system is primed.
When a primer bulb continues to push fuel through toward the engine, it is either because there is a leak in the fuel line or in the fuel system in the engine itself. This is a very hazardous situation that the owner must locate and fix immediately.
Fuel pumped through the lines and out into the boat or overboard is highly flammable and poses a serious environmental hazard. If after a few pumps the primer bulb does not become too firm to squeeze, it is best to stop and inspect the system and make necessary repairs.