Hey horseman,
I have 3 Saito 100’s with many, many flights on them. I have never had a problem with them running backwards because I use an electric starter. I gather you must be flip starting the 100. I had an OS 46FX that I flip started and it always started backwards, so I would flip start it backwards and it would then run correctly. We have a couple guys at the field that flip start their Saito’s and they flip start them backwards. We have both Saito and OS 4 strokes at our field and the Saito’s seem to have better throttle response and seem to have more power, that’s from the OS guys. I don’t have anything against OS 4 strokes, my first 4 stroke was a Saito 1.80 and I had such good luck with it I just stuck with Saito’s. I now have 10 of them.
I hope this helps.