Honda BF 25A weak/dead cyclinder

[gporter]

My low mileage 5 year old Honda suddenly seems to be running on only 2 cylinders; fails to get to normal full power; peaks out at about 2/3 throttle then stumbles at higher settings.

Check of plugs shows # 1 & 3 "normal"; #2 black and wet.

What should I do?

Thanks