i have an 2008 cbr 600rr and the speed is not working right if it says going 130km on the highway im really doing 100km i would just like to know what would cause this to happen

 

Your sprockets have been changed from stock. Probably something like a -2/+1
(front/rear). The previous owner wanted more bottom-end torque.

Check out this website. If you look up your bike, it will show stock gearing.
In your case, it lists your bike as being 16/42 with 112 links to the stock chain.
If you count the teeth on your current sprockets, you'll be able to determine the difference.

Gearing Commander: Motorcycle Speed, RPM, Chain & Sprockets Calculator

Ern

 

If you want to correct the display you can install something like a HealTech Speedohealer. Use a handheld GPS nav unit or something to check your true speed versus the display, adjust the Speedohealer accordingly and you're all set.

I have one on my '08 1000RR and I like it. They also make them for the '08 600RR.