well ... It looks like my idea of padding the transmissions with a pair of 0xFF is not going to work in all cases: when i slowly increase the throttle I confuse the algorithm at the moment the throttle value is exactly 0xFF and for a brief moment I get really funny values on my screen
l.e.: solution was simple using 0xFD 0xFF sync sequence should be safe. Actually any non identical 2 values above 0x02 each would work for our values (max 511 for all that we read)