Re: Small Engines cold air and Performace.
Last person I helped with a China Doll in Colorado got his dialed in with a size 64 main so that might be what you need too if using the same engine. All engines are different tho and you can have 2 identical engines side by side with one needing a jet size up or down before it'll run right.
Also, the jets coming from China aren't exactly accurate so either buy the genuine Dellorto 5mm jets or get some solder and a jet drill kit, this works good because you just solder the jet shut and drill it with the right size bit to dial it in, if it needs to go richer just drill up a size, but to go leaner, solder the hole shut again and go down a size.
Personally I prefer to have several different sized so I can go up or down at least 3 sizes if needed so I can tune for any configuration. I use only genuine Mikuni, Keihin, Weber, or Dellorto jets tho to avoid inaccuracies, others prefer to solder and drill their own and there's nothing wrong with that method either. Your engine don't care what brand is stamped on the jet or what number is stamped on there either, but it does care what size that hole is and it'll tell you when you got it right by the way it performs and by plug reading.
One more thing... These engines tend to make the most power slightly on the lean side so read the plug once you got it running the way you like it to be sure you're not too lean or it'll be nice and powerful but it could overheat or cause detonation... both very bad for the engine.