My little ones started on a LT-50.Good around camp and thats it.Go with an 80 or 90 and just turn it down.The 50's are only good on compact surface.Youll be constantly unsticking the bike.
I 2nd the float levels. Remove your carb bowls,flip the carb upside down, and measure without the gasket in place to the top of the floats.Should be 21 mm.
You going to the Cinders? I change from 310 to 280 going up there.7K elevation.Everything works great. Same jetting on my kids blasters and it works great.