I have power till i get to half throttle then it as if there isnt nothing left. Top speed i think might be 30 mph. It ideals fine and starts right up with no trouble. What would cause this

 

You just posted about the speedo. If the speedo is bad could be a cause of the problem or simply may need to check out the clutches and the belt..

 

so what am i looking for in the clutches?

 

Any thing from a worn/stretched, glazed belt,a belt that has more than 1 1/2" slack when pressed down on the middle with a straight edge across the clutches. Worn rear clutch ramp buttons,front clutch guide button wear.Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse

 

if i take the belt off and rev it up can i tell that way if its the clutches or is that bad?

 

Look at this video and see if it helps you understand how the clutch system works.

 

I changed the belt. But still only have the same power at full throttle as i do half throttle. What could this be? Also clean my speed senser and still speedo dont work.

 

Order the hall effect sensor then for the speedometer. They can go out at any time. If it still doesn't have full power could be carb cleaning neeeded or a new carb kit.Ebay has plenty of carb kits for your Sportsman. Before you mess with the carb,pull the fuel line from the fuel pump at the carb and crank the engine over. Should be a steady flow of gas. If fuel stream is weak you could have a fuel pump problem.