Ive recently brought a cbr 400, had a weeks worth of riding which was all good, now got a problem with the bike, it looses all power after 5rpm. Ive had it looked cant seem to find out what is wrong with it, changed the spark plugs cleaned cabretta! Help!

 

Many things could be wrong with your CBR400, but the obvious thing to check is the fuel line filter if there is one, in your gas tap. It may be partially blocked not allowing a full flow of gas. Also you could try turning the petrol on for a few seconds then off again and dropping the float bowls on the carb(s) to see if there is enough fuel in the float bowl(s). If all is well, then the only other thing I can think of is that the ignition system has a fault, whereby it is not advancing with the revs. Get the manual for your bike if, available and go through the various checks that you can make to help you find a solution. The theory is as long as you have a spark, a sufficient fuel supply and an advancing ignition system the engine will rev through it's full range. Good luck in solving it; other members may offer better suggestions.