Check to make sure all the connections between your carburetors and the airbox are on tight. It could be intermittently causing you to run lean and sap your power.
If you find you have to disconnect anything, remember to build the pipes back from the carburetor to the airbox, they'll stay on better that way.
2010 Ural Patrol (mine)
2009 KLX250SF (hers)
2006 DR650 (???)