Bloody thing wouldnt rev past 8k rpm

this happened to me at the last couple of sessions at oulton last month, but since then i have changed the stator(new one), floats valves, and cdi.
Today i changed :
the coil, but got only a weak spark so changed it back again...still a weak spark
thought it may be the jetting, running 135's changed to 140 but only made it worse at lower revs...so changed back
checked the pv motor on startup goes thru the motions but rev the bike to the 8k max!!! and it doesnt operate, (with or without cables connected)
so i swapped it for another (i carry lots of spares

still the same....
changed cdi back...still the same,,
ty-wrapped the powervalves open (disconnected from the motor)
...still didnt rev past 8k

something is breaking down and not allowing the bike to rev past 8k and open the pv



HELP................i have checked every connection and changed nearly every electrical component