Slow XT
 

I have an 84' XT and the stock gearing is 15/42. I also had speed problems that had to bee chased down. Bike went 90 MPH when I fist got it, the slowly lost top end speed. Cleaned/ Serviced carbs, replaced fuel filter. Got stock size tire and re-geared to stock 15/42. No help on any of that. Found out later it was my clutch slipping in at high revs. $80 labor and some new plates and problem was gone.