I recently bought a sailboat with a Yamaha motor. The motor was sitting in the pervious owners basement for about two years. When I first got it, it was hesitant to start but with the help of starter fluid it went. I used to do around for a few days and then it started stalling and wouldn't start. I replaced the old fuel filter and the spark plug. Now the engine stalls at full power and fails to start again. The last time I got it to start it never got up to full rev. Please help. Feel free to ask for more details.