I have found that the YS 63 and really all YS 4 strokes like high nitro content. I have switched to the Magnum special "DZ" blend fuel with 30% nitro and use it on all of my YS 4 strokes with great results.
I've heard that the bigger Saitos (150 & 180) like the 30% nitro also, but I don't know about the Saito 72. I have never owned one. My guess would be that it would not like the 5% nitro fuel, but give it a try and let us know.

Jim