2500 rpm limit on 50 hp

[sneaks]

my 50 hp Johnson sometimes will not rev over 2500 rpm. if I disconnect and reconnect the fuel lines several times it eventually clears up and the engine runs fine. This problem comes and goes. Could this be fuel delivery or something else? I purchased a new fuel tank and connected the fuel line to the new tank with a barb fitting but haven't tested yet. I thought it may have been drawing air through the quick connect fitting on the old tank.

[boats.net]

Could be a fuel restriction or may need to clean carbs.