I read in a magazine once where they bored a stock 250 to 325cc, installed a heavier crankshaft and raised the redline to 22, 000!
I raced a stock 400cc FZR with just an exhaust and carburetor needles adjusted and it was one of the loudest bikes I had ridden. I can't imagine a 250:)
By the way, here are some pics of my FZR, back in '93.
A week old and I am testing the foot-peg feelers:)
My mechanic, Colin, right before I sold it:(
One last ride before the new owner enjoys it.
No clutch needed, just throttle only:)