china 50cc upgrades

[snicko54]

what is the best china atomic 50cc upgrades ive got 3 that im going to be up grading atm they are backyard warriors and im thinking of making small track in me yard for some mini fun all bikes are stock atm

 

[my67xr]

if you need to rebuild any of the engines you could always go big bore ?
Quad Bike PIT Dirt Bike Cylinder Barrel KIT 70cc Chaly Monkey Honda C50 4 Stroke | eBay

 

[snicko54]

I have 1st semi auto 50cc ,2nd says 50cc but is full manual clutch not sure if its really a 50 or 70cc as I was told some say 50cc but are 70 but im not sure in that I always thought if it was what it is it say 50,70 on the bore and 3rd is a 70cc semi auto just looking for lill mods I can do but im def upgrading the front and rear suspention then its just new plastics and graphics for them all