Saiyans with training like Vegeta are able to rein it in, but Goku never was. After that comes the Kaioken, which is more of a technique than a true transformation. Learned from King Kai ...

So, even though Kid Goku was still strong, having the body of a child limited his powers. Kaio-Ken is the second transformation that Goku achieved in his life. This isn’t necessarily a transformation ...