I would be very surprised to see ring issues only 600 miles in (possible, but low probability). Upon closer inspection it looks like the needle in carb is nicked up in a few spots. Pulled the plug (NGK from the factory on this scooter), it was dry but completely black with carbon buildup - so it appears to be running crazy rich.
Because it was $26 shipped, I just bought a new carb (with electronic choke) for it and will try that first. I'm going to also install a manual fuel switch and will eliminate the vacuum fuel valve (which appears to already be failing, as I have gas coming down the vacuum line to the manifold).
If a new carb doesn't solve it, I'll look at re-ringing it or replacing the topend next. Will post an update later this week
Thanks,
Rob