It looks like there is some extra shine on the output shaft coming out of your transfer case directly next to the sprocket, where you run the rear chain from to the back wheel. Remove that sprocket and I bet you find the broken key.
If that isn't it, open up your transfer case.
the Phillip's screw that holds it on was super loose it almost fell out but I saw it in time maby that is how it got sheared if thats what it is if I tryed to drive it with that bolt loose would that shear it?
Take the transfer case off, unscrewing the 4 bolts to the engine (when putting back on, be gentle, the block is aluminum and can strip). Use your chain to keep the shaft from spinning as you take off the nut holding the sprocket to the shaft. Odds are you can just eyeball the keyways to see if they aren't lined up, or even if they are, you would see the key cut in half. A local hardware parts store (Ace, Tractor supply etc) should have key stock.
I am fairly certain this is the location of the issue. Also, forgot those cheapo chain transfer cases use a machine screw to keep the nut on instead of a nut lol...
Measure your keyway after you get it cleaned out of the broken key. Just put the sprocket back on, line up the keyways and measure the height and width. You can buy key stock by the foot, or pre-cut keys. If uncertain because you have crappy measurement tools, just get the dimensions oversized and grind it down till it fits. Bring the sprocket with you and test the different key sizes in it's keyway. Good luck bro .
You've got the 3:1 transmission there, and a 26 inch wheel. There's not enough gear reduction for a smooth start, that's why it's bucking. Like starting your car off in third gear. 5:1 is what you want with a 4-stroke.
I've had 3 of the Huasheng engines, none of them ever ran well,don't want any more.My predator 79cc and my honda gx35 run r eally smooth but the honda gets hot after about 7-10 miles and doesn't pull hills very well so it will go next.