I’m new to the Colorado karting scene this year also, so I’m not entirely sure what the reasoning is behind Rotax being the only TAG motor run at The Track. I’m guessing it’s because they’re the regional qualifying series for RMC nationals.
It looks like they had some turnout for spec 125 last year. The LO206 also seems to be coming on strong in Colorado. Here’s the results from last year which should give you a better idea of the numbers.