My
JS-90 is on a box stock ST S90. I don't fly it, just run it on the ground and prop it for around 13,500-14,000rpm for my intended purpose. It works pretty good for me. I think it would liven up some with a bigger carburetor. I tried an Enya XF-IV Heli carb on it and it ran the same top rpm as the stock ST carb with Jett muffler but the midrange and idle were horribly rich. Adjusting that carb to clean up the rich idle and midrange caused it to go lean on the top end that the needle couldn't be adjusted rich enough for. I might get a cheap ASP 1.08 carb to try on it at some point.