I have a 1995 Sportsman that idles great but when you get to about 1/4 throttle it boggs and loses all power, it just happened out of the blue one day ice fishing, it ran just fine on the way out but did this on the way in. I have cleaned the carb several times, and checked the airbox, new gas, new fuel filter, and plug. I am at a loss so any help would be great.

 

check the cam lobes. some of the earlier model 500's had problems with the exhaust lobe on the cam disappearing

 

How would i check that

 

I forgot to mention that its a 400 2-cycle

 

Your Silencer is most likely clogged.