Won?t accelerate in forward ?Works fine in neutral

[Charlienofun]

Today when we throttled up the port engine it did not accelerate, it runs fine up to about 1100 RPM then any further throttle and it starts to fall back to idle. Luckily we were just about to get out of the canal and were able to turn right around and idle back to dock. Once we were tied up I found that the engine revs up just fine when it?s in neutral. The Starboard engine runs great so I?m sorta clueless ? where would you guys start?

Oh ya the boat is a 30? Luhrs built in Florida it?s powered by two crusader 454 from 1994