Thank you again guys.
I'm currently running it on a strong concentration of Redex fuel system cleaner. It seems to be ok with it in the tank, weirdly. I haven't done the standard test of up the steep dual carriageway yet though... kind of living in hope and ignorance
I'll let this run through and keep speed down for a while... then do high speed full throttle; if that fails i'll check air filter, replace plug (thank you for heads up on ally head) and clean jet. Yes it has been stood, 3 years and only 1400km. I'm surprised that petrol would gunk up in that time but my other bike is an XR400 which had been stood for a few years and I had to strip the petrol tap and filter from it because it had gone jelly like, so not that surprised. Oh and I'm running this on the 97 ron super unleaded with supposed cleaning additives too.
Many Thanks!!
Hopefully if it all works out someone else will benefit from this too.