Psycho,
I once built a cart very similiar to yours. The one I built didn't have nearly the HP yours has. Mine had an Yahama enduro 175 two stroke motor on it. I was young and didn't have the money for a smaller axle sprocket, it only had a top speed of 50 mph, but got there very quickly.
I always wanted to put a 4 banger on it as you did. Psychocart is a good name for what you have built there. Maybe Widow maker would be a better name.
You might want to consider putting a roll cage on that thing.
Bet it's a wild ride though.