This is my Go Kart from 4939, the seat is a little small, but I ampleased how t turned out, and I like the exhaust I made. It is a little flimsy, not too bad, the steering wheel mount is the weekest part.
This 4939 model seems very popular for building go-kart alternatives; I have seen at least 3 of them. Still it's nice to see all the differences. You did a good job with this one too. It definitely looks like a kart: low, wide and a big engine.