I have been playing with the cheap cheap 70 dollar 50cc kit which im pretty sure is a replica of a stock euro cylinder. Anywho I too was playing the stock vario and recently went with er3 and a doppler er86 pulley
So far it rips super hard. I soft seized on the last good day of fall. I knew jetting was off but wanted to go for a short loop and that was it. But got another kit cuz hey its 70 bucks and the last one held up for a year and a half with a high rpm set up.
Don't know where I was going with this but cheapo 50cc has been a blast and hands down one of my fastest builds even before playing with fancy varios and clutch pulleys