Well it was the TPS. You were absolutely correct. After messing around with power valves, exhaust pipes, cables etc I plugged in my spare carbie and the valve cycled to hi and lo just fine.
So new RULE No.1 for me when problem solving is to try the simplest problem first. Looking forward to track day now to give her a run. Thought I might have to take out the mc18. Blisteringly quick but the suspension needs a lot of TLC which is what I would need if I tried to outbrake anyone while riding it. 
Thanks all for the help,
Damian