It is a cdi ignition. The scooter is a Chinese import using a 139qmb engine. It's branded as a Baja Sun City SC50, but it's the same mechanically as all the other 139qmb scoots.
Symptoms are a high rpm, full throttle misfire when cruising at top speed. Spark plug looks good. Full throttle power seems good until I get up around the current top speed.
I installed a big bore kit (and adjusted the valves while I was at it), which also included high-flow air filter (uni filter), high flow fuel filter (visu filter), new main jet, and new roller weights for the transmission.
I've been playing around with the roller weights to help with balancing acceleration and top speed, and like how it feels except for the misfire. I also have a main jet kit and experimented with different jet sizes to see if it was starving for fuel, but it ran slower when I put a larger jet in it, so I went back to the jet that was included in the kit.
One of the reasons that I wanted to check it with a tach was to see if I might be hitting the rev-limiter (I think factory limit is 9k?). The miss doesn't sound like that tell-tale rhythmic rev-limiter sound that I'm used to hearing on cars, but this engine doesn't rev that fast either...
I know that I can get an aftermarket cdi that doesn't have a rev-limiter, but I don't want to push this made-in-china engine too hard. If my rpm's are too high, I'd rather change the rollers a bit to bring them back down instead of blowing the engine.
What kind of symptoms would a bad cdi give?
Give a man a fish and feed him for a day. Don't teach a man to fish...and feed yourself. He's a grown man. And fishing's not that hard.