I have a 2005 Polaris sportsman 90 new carburetor old air box when I give it has it is wide open if I cover some of the air intake it will run a lot better any ideas

 

Sounds like it's too lean,either jets clogged or too small.heck that fuel flow is good also. Make sure the air screw is about 1 1/4 to 1 3/8 turns out.This you can fine tune when engine is warm. Filter in good shape? Are jets the same size as in the oem carb? Plus on these aftermarket Chinese carbs I'd always clean one before I installed it.Some have reported dirt/trash in the bowls and some openings clogged.