all or nothing

Change in seasonal weather? Water in Fuel? I get personality out of mine with season change. If my carb is too rich like in the middle of summer sometimes it will load up when idling at a stop light for a long time. I finally got things dialed in to where I can finesse it with my fuel adjust screw. That was fun !

Mine acted up once on me and I was sure there was something in my carby once. Was fixing my gas tank tubing and flip the bike at a weird angle the carb cleared right up after that lol. Carbs on any of these small engines can get finicky sometimes.

Working in a small engine shop I cannot count how many times I cleaned out a carb .. This is different than your scenario I recon. These were engines that had set for months fuel never drained motor never started. I would do everything short of vatting the carb in some cases even vatted them. Only to have the carb back off twice to take a very fine wire and poke the jets out again.

Also it is very hard for a newbe to know for certain when they are rich or lean on these Morini's I got to sharpen my ear in ...in the beginning.

Didja change oil ratio any lately?

Maybe it's your clutch. When it's hot, does it feel like its engaging early?
I remember with my old clutch after some hard laps it would start to engage 500 rpms sooner.