2010 Sportsman 500 HO carbureted . Bought new in 2010 now has 135 hours on it. Ran great until about 125 hours then it started bogging and running poorly above 3500rpm when warmed up. The warmer it gets the worse it runs. I replaced the fuel pump, fuel filter, air filter, spark plug, adjusted valves, checked compression, and replaced the black rubber tube from air box to the carb. Here in lies the problem. If I remove the air box and black rubber tube it runs perfectly and screams to 6500 rpm. If I slide just the black tube, no air box or filter over the end of the carb it immediately starts spitting and sputtering when I give it any throttle. Remove tube it runs great. The tube is new and not cracked or collapsing. The tube is big enough inside to almost insert my fist yet the machine will not rev if I install the tube. Anyone else have this problem?