Hmmm defintaely a strange problem. Does the speedo read accurately, or is it way off? Definately does not sound good.
The XH XR's have a modified cam and head. I'm unsure about the series 1's, but the series 2 have a different intake manifold, computer, airbox...
Welcome to the boards BTW:s5 :s5
Good to see another XH owner, XR owner at that on the boards. Look forward to seeing some pics of yer baby...