A good friend of mine (Elliot Burgess) use to race an RS250 in the 90's. I asked hime what he got from his bike...

When he got his 250 from Japan it had 68Bhp. The team set it up and got 73/74 ish/Bhp, tuned, it didn't make any more BHP, but gained so much more mid-range! loads of torque! i.e Say 50 bhp at 9000 rpm before, it was nearer 60Bhp after a fettle! All down to crank tune, ignition, airbox, new heads and pipes.

Also to note the bike was only 100KG!!!
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Thompster (aka Simon)