My xt 600E is 3ux swiss model manufactured 1991. It has 39hp-reduced power (other models 45hp) and I wanted to know what I should do to get 45hp. My friend has 2002. model with 39 hp also. Same problem.

As far as I know, the only thing to change is the intake rubbers ('ansaugstutzen'), between carb and cylinder head. There might be some differences in airbox and exhaust system too.
As you have a Swiss bike, do you live in Swiss. If so, easy to contact kedo, KEDO - Performance Products, in Germany, they'll be able to tell you.
In their catalogue I'm sure there is intake rubbers for the detuned ('gedrosselte') and the 'open' version.

Auke

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Auke
http://aukemarieke.blogspot.com