Costerito, some of this I said in a PM: This is actually my old bike. It's a fantastically reliable bike, the guy I sold it to is going back to the states, I might buy it back from him! Although I'd love Sundiro Honda to manufacture the CBF250 again, and in China, I'd buy it in a heartbeat, especially if they could get the price right, as Yamaha have failed to do with their YBR250, which is way too expensive IMO.

Break it in how you mean to ride it the rest of it's life, but change the oil often! Bike should be fully run in by 1000 kms. First oil change at 200kms, if you haven't done it, do it now!

Top speed is an indicated 123kmh, red line in 5th gear.

If you change the exhaust you'll probably only loose torque and gain minimal power, so probably not worth it, unless you can do it really well with a good quality smaller sized muffler maybe designed for a CBR125 or similar. It is worth changing to a Japanese NGK spark and maybe balance the carb to run on 97 fuel, with a clip on air filter and remove any heavy stuff like the center stand. I'd find lower bars and find old CBR pegs for the bike too, maybe there is some old race stuff around at Tianma circuit in Shanghai, as there was or maybe still is a Chinese CBF150 championship.

Changing the tires to bigger sizes may just harm the handling or slow down the top speed, personally I'd keep the tire sizes stock, as in I'm from the UK, we believe that you shouldn't change the stock tire sizes and try to run the same brand and pattern front and rear. I might suggest you could think about going for Sakura instead of the Duro, or use imported western Michelin or Bridgestone. I could knee down easily slow speed on the Duro's no problems though.