Hi, boy, If you use a small rear shock, the rear of the bike seat will lower. looks ugly. so change a rear shock. the same length while little soft. the adjustable rear suspension will be better. you ride on and adjust it from 3500lbs to...unitl the chain do not eating the swingarm.
Gee. who said China only have cheap bikes !!!
You came to find a China 140cc oil-cooling minibikes.
the price is around US dollar 1200. then you will find it is suitable for you.
If you only get cheap bikes, cheap in the end.