2006 Bruin 250. Will only throttle to 1/2 - 3/4 throttle then cuts out. Thought it was carb main jets so I put on new carb. Still has issue. Found I can remove the air cleaner cover and it will throttle up full. Not remove air cleaner, just cover. If I leave the cover on I can shoot some air down the intake tube and it throttles up full. Just doesn't like cover on. Is there some kind of vacuum that helps assist intake or a PCV valve or something similar I'm missing?