Yea basicly you got a carb air leak, or some other fuel problem, like a non vented tank cap (try and ride with it loose?), Or similar.
the engine should work fine from day 1 when setup properly, it just goes from reasonable power to fun power after break-in, And then up to dangerious power once you start modifying it and add an expansion exhaust etc
Critical break in is the first 1 gallon of gas, Idealy you want lots of oil, and to run it hard, but intermitantly. (ie got WOT now and then and get some high rpms, just not continiously) and then it seems to gain a little more power over the next 4 gallons, then its broken in.