I wonder if anyone could give me a hand diagnosing this problem. I'm unlucky enough to be on my third 125 within a year, having had to get rid of a couple as the problems cost more to fix then they were worth. At the moment I have a GZ125 and it's not without it's faults.
At the moment it's tending to hate third gear and when I try to change it up from first (about 10mph) to 3rd (About 25mph) it will intermittently begin to splutter and drastically loose power or just shut down altogether. After a couple of minutes it may start again although sometimes the battery will just click. So far I have changed the battery (about a week ago), firmed up the rectifier connection, fully cleaned the carb, changed the spark plugs, adjusted the valves, changed the old drippy fuel tap and the gasket as it was leaking and the oil more than once in the last month but still the problem persists.
Two possible issues maybe the fact that after a drive or at turning on the voltage is at 13.6 but as it revs it falls to 12.5. But then the battery will show the 13.6 after returning to idle. Also, when changing the oil, a spring and threadless bolt fell out the engine. I've looked at manual and have no idea where it came from (picture attached).