ORIGINAL: GBR2
Another student had a 60 size evolution in his plane that did run OK except that the low speed needle valve needed to be closed far lower than the installed stop allowed. Once that was defeated, the engine transistioned nicely and ran strong.
This is normal and explained in the manual. It is easy to reset the limiter for a new range. I think it takes a 2mm driver. The manual also explains how to remove the low speed limiter altogether. The limiter on the high speed needle knob should be a press fit pin. I took care of that with my Dremel.