Update
Problem found! My 912 was running better apart from a few stumbles on takeoff.
Witnesses on the ground were at odds as to whether it was a lean miss or flooding but definatly not developing power on two cylinders.
The floats and float levels had been replaced and checked multiple times,so I decided to replace the float needles (again) the fuel hoses and banjo fittings were removed and everything blown with compressed air.
On testing fuel ran out the r/h carb filter,the carb was stripped again,blown out and visually checked ,nothing visable.
A bit of wire was wiggled in the fuel intake side of the needle assembly and blown again.
An object was observed flying out the port! whatever it was, it wasnt getting blown out untill it got broken up.
Reasembled and test flown, consistant idle,smoother running no more stumbles!
I now have had around ten hours of trouble free flying.
I was dealing with at least two seperate issues which have been resolved and can now really start to enjoy relaxing flight
The moral of the story,NEVER ASSUME .
The carb had been stripped blown out multiple times with the debris still in place,perhaps a magnifying glass should have been used,or as been suggested, pressurise the fuel system and the fuel flow flow visually checked from the needle seat, an obstruction may shown up as an irregular flow pattern.
I hope this lesson may someday save someone else a lot of grief.