is it possible to fit an xvs 250 engine into an xvs 125?they look pretty similar but i wonder if it was possible would i have to change the braking system as it would obviously need more stopping power?

Do some measuring. ie- mount holes/ width/ sprocket chain line up... angle of exhaust out of head.

I'm not 100% sure but I think the only difference is the top end? Like the barrels etc?

But surely the price of getting hold of the 250 Is close to that of just buying the actual 250 bike???

Buy a 650 instead... by the time you've paid insurance the 650 will probably be cheaper