well it all depends what you want. you say youve just bought it, so you havent ridden it much, so how do you know you need more performance? the 250rs is a lovely motor in a sweet handling chassis, its not blisteringly quick, and its not a race bike, but for what it is, a lithe pleasant 250 single, its bloody lovely. tuning the motor will essentially change everything about it, if its got more power, then it might benefit from better brakes, and then you might find that you want better suspension, then you find youve a great handling bike with fab brakes but you need more power etc etc etc, just saying 'i want more performance displays a bit of an ignorance as to what performance is. i could make my bike go faster accelerate better handle better and stop better without spending a bean. i would go and lose 5 stone and bingo, not a spanner laid on the bike. you see performance is about much more than power, you could go for a big bore kit and that might give you a few extra bhp, but the chances are that alone it wouldnt do much, so up the compression, some head and valve work, a nice cam, a decent exhaust, and congratulations, youve just spent a grand on a 500 quid bike and made it worth 750 quid and it will now keep up with a 400 superdream. you see what im saying, power is an expensive product, the more you want the more it costs, and at the end of the day you will end up with something only marginally quicker than when you started. anyhow, the one tuning mod that i can give you for a cb250rs that people will agree with and that will genuinely give you more power and torque and not affect reliability, at least not engine reliability, is to fit an xl500 engine into the frame and do away with the 250 lump completely. back in the day this was a quite common modification and when you look at the cost of tuning an engine, the 500 motor swap becomes incredibly good value, especially if you can find someone to buy your surplus 250 engine.
