Like Don said "baby it" for a few hundred miles. After I put a 70 cc kit on the PUCH I ran a 32;1 mixture and never over 3/4 throttle for a hundred miles. Then occassion wide open for short bursts, then back to 3/4 throttle. It is basically like this, baby it for several hundred miles (at least 300) then you can cruise around w/o a worry. I usually cruise at 3/4 or 7/8 throttle on level and wide open on the upgrade. I never have it wide open going down hill (you are looking for real engine trouble). How long is enough. I don't really know, other than to describe it as this, the sound of the engine will let you know.
With my Derbi, I babyed it for several hundred miles. One day I (around 350 miles) suddenly noticed an improvement in preformance and sound of the engine. MOPEDS are like high preformance cars, break them in according to the manufactures instructions and they'll run well forever. Break them in at full throttle and 10K or 20K down the road you are rebuilding the engine. (Testimony is my '86 vette I bought used w/60K. It is still just as fast as it was the day it rolled off the truck in Richlands, VA according to the former owner who recently drove it). Rich