How does this work? want to get a bigger back sprocket without affecting the top end that much suggestions on how many more teeth i should get? it does 85 top speed lol

 

Stay stock. You need to go slower with your stock sprockets first.
You are flying in those pics.
Get 15MPH steady first then think about gears.
If anything try just -1 , +2 or 3 to keep the same chain and you will still have 70+ I think

AND KEEP YOUR FOOT ON THE BRAKE

 

Your on a 125 man, getting retarded sized sprockets isn't a good idea!

Jeremy's right though, gotta have BP before you need to consider that stuff though.