Relax, it has been scientifically proven that freeking out about ped problems significantly impairs your ability to operate and enjoy your ped. : )
It sounds like your smaller jet improved things somewhat, so going in the opposite direction would most likely make it worse.
Have you tried running without the air box and/or filter to see if you still 4 stroke. Often, as you increase rpm and the need for air, the existing set up will restrict the air flow enough to cause the mixture to richen up.
Try this and post results.