Verify that the Clamps are Tight, to the Rubber Isolators between Carbs and Intake Manifold... 2 Isolators, and 4 clamps total.Bike runs well under normal circumstances. As the temp rises to where the fans kick in the bike still runs well. When I shut the bike off for say a lunch break it will start but will only idle. I cannot rev the engine up over 1500 rpm .It sounds and feels like there is water in the carbs. Thinking that water was the problem I poured methyl hydrate into the tank. with no immediate response.... Cold starts are not a problem .Only when the bike gets overheated does this problem show it's ugly mug.
When they loosen, Air will leak into the joint, causing the fuel-air mixture to go Lean... The lean condition gets worse when the engine is warm; Does not affect Cold (Rich) start condition.
The isolators harden with age... I replace them after 10years, at which point they are so hard that they no longer seal; I also re-install them using "K&N Air Filter Grease", for an air-tight seal.