I just purchased a SUNL 107, fully automatic, for my kid. I read up on quite a few different brands and etc. and this I think was the best for my money.
I will need to tighten that screw quite a bit, my kid is 7 and will need to start him out slow, but when I tighten the screw and nut at the lowest point, it starts off slow, but within about 25 feet, it is really moving, about 15 miles an hour easy. And naturally when I take off the nut and tighten it down, it will just vibrate loose. 15 isn't fast, but he is a beginner and would like him used to it before he is going that fast.
Does anyone have any suggestions or help so maybe I can get this thing down to about 5 to 7 mph?

 

Well first you can try using Locktite on the screw. Or maybe take the nut off and replace it with a small spring to keep Tension on the Screw.Hope this Helps

 

Make sure, its metal on metal if you use locktite, also make sure you use green lock tite and not red. If you use blue, you might need heat to remove it, or strip the head trying.

 

Thanks for the advise. I think I will try the spring first and see how that works.