I just replaced the pucks and flipped the second gear clutch on mine, and put a fresh top end/pipe one. Geared tall to keep rpms below 8500 rpm. For me this is a treats piston port kit/head, mlm peoples sidebleed pipe, 19/37 gearing. This is the “fast but reliable” setup I was recommended to follow, without having to worry or mess with shimming assuming you put them back in the right spot. I did not the first time and it wouldn’t roll backwards. I also didn’t put the roller bearings against spring tension so the transmission never engaged lol.
From my understanding, once you mess with aftermarket cranks, you need to nail down the low tolerance shimming part of the equation. Supposed to be easier with the official tool but it’s rare, I’ve been hoping someone holding onto it sends one to MLM for reproductions.
With that setup so far not really tuned, I get 74cc e50 kit like acceleration off the line in 1st. Hitting low 40s. My other ZA is geared even taller at 20/35 so I guess it might last longer but this season will be my first with ZAs, I’ll probably be posting here on results.
Detroit Moped works used to be the go to but they only do small/quick local repairs now. The mods mentioned above are easy to do though, just need to make sure you correctly take off the right hand threaded nut, and grab the second gear locking tool from treats. The tool the holds the sprocket isn’t worth it, just use a 8mm socket, it’s useless once you change that front sprocket. (edited)