Upgrading a 250

[ta borom]

So, i was thinking of boring out an xs 250 to a 400. Is it possible. I've checked on the workshop manual and the only differences are piston sizes and cylinder barrels.
Would a swap fit straight in? And if so, do you know from where can I purchase at a reasonable price please?
Thanks guys

 

[drewpy]

the 250 has smaller valve gear and a smaller 32mm carb/inlets

A 400 top end will fit no probs, but you'll need to raise the gearing on the back wheel.