The engine is a 1987 Yamaha 200 hp. There was a rebuilt powerhead put on it in 2000. I had no problems starting it til yesterday. It seems that ther is no spark to any of the plugs. I had the engine running for a few seconds but it stalled. I then tried to start it again, and it fired but didn't start. This happened several times. I tried to start again and then it wouldn't even fire. I let it sit for a while, then it started. Went for a ride, brought it back, shut it off and had no problems starting it several times. went to the boat today, started it, after a couple of seconds, it stalled. tried to start again, same thing as yesterday, fired a few times but would not start. I didn't have time to wait around and try again. Any ideas as to what could be wrong? 