The problem still persists, although it has changed a little... I have tried:

- cleaning out the carbs
- cleaning out the fuel tank and fresh fuel
- new plugs
- cleaned air filter
- cleaning out the fuel tap (full of crud)
- checking the coil primary and secondary for resistance (both are equal across both coils)
- checking the charging rate
- checking the new good quality and fully charged battery
- both RC valves rotate when blipping the throttle

The symptoms are that in the early gears the bike will pull through to about 7500 rpm and then refuse to pull any further, in the later gears 4,5,6 it will not pull past 4500. It sounds like it gargles, similar to when you hit a limiter.
Tickover and bench running sounds OK, there may be an issue but there is not enough load to show it up.
The plug chop shows as dry but maybe a little rich, not black sooty but definitely not brown, somewhere in-between.

Any advice gladly taken as I am running out of ideas!!

Cheers