I agree with Pat. Also keep in mind that all Tag engines are expensive to maintain. The 2 most common are Rotax and Leopard. Rotax has programs all over the country and the world, but the costs can be very high to participate in some of those events, and the rules are quite stringent. As a Tag engine, it is a fine engine, but it does take a little more to learn the finer points of tuning the carb, as you need to change jets vs. simply tweaking a needle setting. The Leopard is also a good engine for Tag, and is quite popular and fairly easy to tune. There is plenty of maintenance to be done to that engine as well though, particularly with the clutch.
Those are the 2 most popular packages around the country right now. There are others with regional popularity that could be candidates for you as well. Like Pat mentioned, figure out where you want to race first, then pick the engine package.
Best of luck!
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