Will not start

[belleair2]

I have a 1993 200hp Yamaha. A few weeks back the engine would not start. It would crank but not start. Call my mechanic and he unplugged a few connectors under the cowling and it started. Said it might be some corrosion. The next I went to use the boat ( a few weeks later) it started right up. About 3 weeks after that we went to use the boat and would not start. Same problem just cranked. Removed the cowling and did the same thing. Still no start! Any suggestions. Thank you. Nick

[boats.net]

If it has loss fire to plugs then need to test ignition components, wiring, key switch and landyard switch.