I have a pair of QT50's. Mine has a YT60 cylinder slightly altered exhaust and a K&N style air filter.
The moped runs great but soon after it heats up it starts to bog and then in the middle of giving it gas it suddenly stops and seizes. It almost throws me over the handlebars when it happens.
I turn it off for 5 mins and it runs fine again. I've also turned it off as I feel it bogging however even with the run switch off and ignition off it still continues to run until it dies slowly.
Its very weird I was was wondering if it could have something to do with the CDI or the first or secondary coils. I know for a fact that it's not the piston or rings or the ignition kill switches.
It acts electrical.