I feel like you would benefit from a temp gauge to see if you are spiking in temos.
My best guess tho is either a recently developed airleak or an overlooked one. Bing carbs like many clamp on carbs have troubles sealing up at the intake. A head air leak is super easy to get if you have taken the head off a few times and reused the head gasket.
Reusing any gasket can be asking for trouble honestly. If you see any gasket stuck behind on a mating surface, you would be best advised to remove the material left and replace the gasket with a new one. I realize this is not always possible or cost effective, but best practice I would say.
Mopeds like any vehicle can be run at WOT for a while, but temps will always start becoming an issue. Air cooled engines especially in high temp areas, are going to have a harder time keeping cool. Race built things are designed to run at WOT or close to it for extended periods of time and not blow up, but they still can and they will almost always get rebuilt before the next time they hit a track.
The only thing you can do is keep the engine free of air leaks and keep it lubed on the top and bottom ends, and hope for the best.
Probably not a big thing in FL, but I would avoid WOT on large downhills. That's a good place to blow up your engine.