the bike revs as normal when standing still, but when riding hard seems to be missfireing all plugs are good,and light chocalate brown, it feels like the jetting is wrong but it isnt and the carbs are cleaned after every other meeting and are ok. it has a bdk cdi box as its a race bike as anybody else had a simular problem as i think the box is at fault !

Cracked carb mounting rubber? I had this problem once and it had the same symptons. Took me ages to sus it out, the carb rubbers did not looked cracked but were perished.

Check the battery is really good as at high revs the cdi/ignition uses a lot of power.
Also check if the tank is rusty & bits of shite are blocking the filter as I had this once.

Hi, makes sure the tank breather isnt blocked.
Cheers
Ian

Thanks for the replys but still not cured,cleaned tank, fuel-tap new fuel filter,checked fuel pump,stripped carbs, all spotles still the same,when holding the throttle flat out it revs too the max then go's to 10000rpm

Ok so fuel seems ok .... how about electrics ???

Ckech the ciols ... can you swap them for another pair. Make sure the plug cap and HT leeads are all good and not got a weak connection anywhere.

thanks for the info problem solved, old ht leads, put some new leads on and she's singing again, :D

Cool glad it was a relativley easy problem to solve