Glad to hear changed the air filter worked for you.
I had almost the same problem, when it was raining heavily or had just rained heavily, I had problems with my scooter running. It would often just turn off when I was waiting at a red light or just accelerating from a red light. If I did manage to get my scooter going from a red light, there was no power loss.
It was just scary having your engine die when the light turns green, as I'm sure a lot of you can understand. Especially if you aren't on the far right of the lane.
I was told by my friend at the Kymco warranty shop in Hsinchu (or is it Hsin-Ju) that the "Ignition Coil" is often the problem in my case, even on new scooters.
I went to my scooter parts distributor in Zhubei and ordered a new ignition coil with a new spark plug lead for about 680NT and put it in myself. It's a real easy job, just take out the seat and compartment, take off the 2 nuts holding down the ignition coil and disconnect the 2 wires that connect it and the spark plug lead.
After changing my ignition coil, never had problems with the rain since.
However, with your scooter, I can easily see that the air filter that would have been the problem. Often when scooters don't have much power and have problems getting upto 60+km/h, check your air filter and the air box if it's properly sealed.
Found this out the hard way after I took apart my carb to clean it and my air box. When I put it mostly all back together, with a new air filter, I didn't put the cover to my air box back on and tested my scooter and couldn't figure out why the engines RPMs had troubles going higher or being steady over 3000. Ended up taking apart my carb again to
see if I messed something up. Everything looked fine, so I put the carb back on and this time put the air box cover back on, and that fixed my engine RPM troubles.
I guess lastly I'll finish up with what tommy525 called a "distributor". In my shop book for my scooter, it's called a "CDI unit". It controls the firing of the spark plug, which gets it's timing from the alternator/generator. Most scooters have them, even if they aren't fuel injected. My isn't fuel injected and it has one.
I know when I saw the word distributor, I saw a picture in my mind of what they used a long time ago in cars and motorcycles. A round thing with your spark plug lead(s) coming from it and inside a bar that would spin around to make contact with the lead(s) to deliver the spark. Can't remember when they stopped using those, as I only got into
engines in the past five years or so.