I am original owner of 2005 2 stroke Mercury Saltwater 150hp that has 300 hours on it now. Ever since I got it, it's been extremely hard to start. I make sure the primer bulb is firm, turn the key, choke, put throttle forward half way and the engine cranks fine. After several attempts to start, the engine will stop cranking while the key is turned and it makes a humming sound until I turn the key back to off. This will happen a few times and then the engine will start. I can immediately turn the the key off and the engine will start with no problem. Anyone have this problem and what is the solution? Thanks.