So, I own a VGA Digita (Longjia LJ50QT-2L), and I have a minor problem. I was out scooting a couple of weeks ago when the engine died on throttle. Couldn't start it up again. I then changed the spark plug, and the scooter once again would start up and run fine. After driving about 50 km though, the engine died again during throttle, couldn't start it up again. Then, a couple of days later, the scooter now starts and runs fine again. Any idea what the problem could be?