The Yamaha was the mainstay engine for many many years, but it’s popularity is waning with the advent of newer push-button start engines that are more reliable, more competitive, and easier to run. There might still be some local clubs running Yamaha classes, as tons of people have them and there is still a desire to race them. If nothing else, it’ll make a good practice engine.
The two booming classes right now are LO206 and KA100, which are growing rapidly in many areas of the country. As a newbie, you can hardly go wrong with a 206 package. It’s cheap, easy and a good place to start to learn good driving habits.