Jinling 21-b problems

Hi,

I bought a Jinling 21-B not too long ago, when i got it the battery regulator was disconnected and fried, obviously causing the battery not to charge, so i bought a replacement and in the meantime i cleaned out the carb, i fitted the regulator and it seems fine, i could see the voltage going up as i reved, i took it out for an hour in the week and it ran lovely, i started it a few times yesturday and it started first time, then i took it out and it was kangarooing, so i put my clutch down and started to brake then it cut out, how it used to with a flat battery! so i pushed it home and tried numorous time and it would not start, the battery symbol was flashing, so i put my meter across the terminals on the battery and it read 12.71V DC, so now im confused!!! whats going on!!?