I use AMSOIL 100:1 2-stroke oil. I mix 2-1/2 oz. per gallon of gas, which is what I was told by Cosmo motors, the importer of my Kinetic Magnum moped. I have used this synthetic oil since the moped was new. I've heard that it is not good to use "real" oil and then switch to synthetic later on.
AMSOIL is a very good quality synthetic and I've had no problems with it fouling sparkplugs or causing smoke or anything.