Thanks for the suggestions, all appreciated

The feeling when riding is not a leaning off but a kind of 'fatness' the bike is struggling to deal with. .....hard to describe but it feels like the bike is drowning rather than being strangled (lean), if that makes sense. For me a lean condition feels like a relatively smooth dry vacuum off the throttle...no one home, but rich is all vibration and hesitation eventually clearing. The plugs also read rich and the rear of the bike has a splattering of mixture after a reasonable run.

If it is the float height then it would seem to be too much fuel in the bowl, which may be causing the problem but it only happens on an extended closed throttle from high revs. This is why I thought it must be the vacuum created by the high revs drawing fuel into the bike somehow thru a closed throttle.

Will hopefully have the parts and time next weekend to work it out.