Doesn’t your lawn mower have a choke? If it does, you’re either not closing it, or the linkage is broken. When you try to start a cold engine, you need more fuel. That’s what you’re giving it by priming it continuously. What should be happening is, the butterfly valve for your choke closes, inhibiting the flow of air into the carburetor, thereby making the air/fuel mixture rich. As the engine warms up, you gradually open up the choke until the engine can breathe its normal air/fuel mixture.