Trouble with Rotax 912ULS

All checked and fine.

No vibration and rpm steady.

Thanks but fuel hoses cockpit side of firewall had already been renewed before, and there was no trouble then.

Thanks Jacques - rubber below expansion tank checked and was OK.

Thanks - all checked as you suggested. Aircraft flown for 1 1/2 hours at varying rpm, descent / climb etc etc and flew beautifully . Two days later on short flight and on the cruise 2 second stutter then gone again and did not repeat - rest of flight fine ....,