1 plug not firing need help

[passingwindII]

i have a 40 hp 3 cylinder yamaha might be in the mid 90s that one of the plugs isn't firing (#3). the last i ran the boat in the water was about 2 months ago. I've been running it with ears on about every 2-3 weeks. the #1 plug sparks with a good pop. the #2 sounds like it might be a liitle weaker and nothing on the third.. Any ideas. i've already changed plugs and switched the coils. plugs is wet i do get fuel.could there be anything in the ignition that would cause this?

thanks in advance for any help givin
steve