Presumably its a modified saw, so without knowing whats been done, the best answer is whatever the carb allows. Generally racing with gas saws, the saw is tuned a lot leaner than you would for work. I would start by tuning the high right to where the saw barely 4-strokes, then go slightly leaner if u want, compare cut times with tuning adjustments. But it will be running hotter, so you gotta be careful. I run 25:1 or so for the little bit of racing ive done.