could you please tell me how to tell if my cbr125 is restricted, it will reach 50-60mpy quite easily but it'll go slower after. my friends' cbr125 is the samebike but he's seems a little slower and less powerful, mine has 1533 miles on the clock and he's has 437, so i was wondering if he's seems a bit less powerful due to the low mileage and that the engine isn't quite broken in, i would appreciate and answers. mahy thanks

tony, December 2006

Even with added "race parts" you'll still be lucky to see anymore than an extra 2 - 4 mph out of it. I use the CBR125 engine in our MinimotoSidecar (British Championship Winner - 4 stroke class - 2 years on the trot). We've had allsorts attached to it. Mikuni 32mm Flatslide carb, Dellorto carbs etc... and NONE of em give more power than the stock carb. Seriously, stock carb is about as good as it gets with the CBR engine. Exhaust change makes it sound nicer, doesn't add any power, just shifts the power around a bit to give a bit more grunt in the midrange... CBR's biggest problem is weak midrange. It's bottom end is fine, top end is fine (if a touch on the slow side) but midrange it can easily be beaten by an 80cc 2 stroke.

Get an unlimited CDI (you have to import from Tailand, Indonesia or Malaysia for this usually), pick any exhaust you fancy (makes little difference). Port and skim the cylinder and head. Lighten the flywheel. Regear it. That's as good as it gets.

Marci, December 2006

yes his engine will still be tight ,thats the reason your is quicker tony.i work in a bike shop and that is about the top speed you get out of them they are not restricted by any single item only the gearing (sprockets),the rev limiter built into the cdi unit,the exhaust system and the carburettor all these thing are slowing it down the only way to make it faster is to replace them with after market race replacements ok.hope that clears it up for you.

adam bike doctor, December 2006