Taipai scooter assassins has smooth bosses and also brand name and cheaper clone gy6 race variators too. I fitted the cheaper clone race variator to my agility 4t 50cc, changed boss, fitted 5,5g rollers, cut the cdi, put in an 82 main jet and get 50 on a good day on the flat, 50+ downhill, with better acceleration too. Much better now. Got boss direct from scooter assassin site, got variator on scooter assassin ebay site, think was about £7 for boss, £18 for variator.