OS 61 FX with stock muffler is like 24 oz. OS 91 FX 2-stroke actually a little lighter. Saito 100 4-stroke is less than 21 oz., lighter than OS 61 FX. Modern 4-strokes are really light, and the fact their muffler don't have to be so big translates into further weight saving. Saito has about the best displacement-to-weight ratio out of any stroke.