Re: 48cc vs. 69cc.
In defence of the 48cc, both i have do not vibrate at all so bolts dont vibrate loose, make your own idler out of a skate wheel get a good chain get it straight and true and you can forget about it.
Get new studs spring washer and loctite em, the motor wont move.
No leaks! Make youself new intake and exhaust gaskets.
Touch wood i have not done anything to my bike for 3 weeks maybe more just fuel.