this kit is pretty much the most popular one:
Also, one of the best things you can do is to disassemble, clean, and then reassemble the kit before you mount it on the bike and run it. The little kids that make these in china might of dropped a screw in the crankcase and oftentimes there are metal shavings in there etc.
Johnny law can't tell the difference between a 48cc and 66cc, esp if you remove any badges/labels. Externally, They are almost the same thing