1997 Yamaha 30 HP running poorly (Need Help)

I have a 1997 yamaha 30 horsepower 3 cylinder outboard engine and it has started to play up,
When running down the river sounds like its missing and then it got that bad it was at full throttle and it couldn't get up on a plane,
I checked the spark and seems to be ok and when the engine was running i pulled off the top spark plug and it died and then tried the same thing with the second cylinder and it done nothing at all kept running like it was,
So i cleaned out the carbys and changed fuel hose and got new fuel and put in new spark plugs and still has the same problem,
I think it might be only running on 2 cylinders, The middle one might not be running, (Not Sure)
I am at a loss, Can anyone please give me any ideas of what may be causing this problem, Thanks.

Do a compression test on it.----Could also be a problem with crankcase compression , reed valves.

I think the bottom 2 cylinders are not running, I am waiting ti receive a compression tester, is there a gasket needed if i replace the reeds?
The engine is a 30deo, It might be a 1996

Agree with Racerone - do a compression test. But before tearing the engine apart, I would try to decarbonize the engine using something like Sea Foam or Yamalube Ring Free. In many cases, just blowing out the carbon will free up valves and rings and help open up the carbs.

Do you know what the compression should read?
The 3 cylinders are running 90 pound

I think that is too low, but best check on the Yamaha Forum on this site. Go to the top of this page, click on "Forum Home", then click on Yamaha Outboards.

To do the compression check correctly, use a screw-in gauge, fully charged batteries, activate the kill switch, remove all plugs, throttle wide open, crank for at least five seconds on each cylinder.