Why wont my motor hot start?

I have a 3hp briggs and stratton that is a water pump it will only start on starting fluid and when it starts up it surges for a bit then goes to normal there is a slight crack in the carb to the cylinder intake and the motor wont hot start only with staring fluid can i adjust more fuel to compensate for the crack id like to not buy any parts like a carb cuz the motor not that special i just want it to start on gas with the pull starter