Hi RCPat
I have this plane with a Saito 100. I made the mistake of not adjusting the low end needle on the carb after I inverted it in the plane from the test stand. (upright breakend). I was very dissatisfied with the performance. I cut the rear tank support out and lowered the back of the tank. After it stalled just before a low hover attempt, it ripped the firewall out when it hit the ground. While I had it apart, I lowered the firewall about 1 1/4" making the exhaust channel shallower.(not used anyway with a Saito). Lowering the tank stopped the engine from filling up with fuel and bending my spinners trying to start the engine. Fixing the low end needle makes it a great plane now. Two of my friends have a YS-91 and a OS-91 and have not lowered their tanks and they seem to run fine.
Onetankjcs