Its supposedly the Premium carb offered by GruBee's 48cc kit. Has a built in choke cable and a mixture screw along with an idle screw. The new NGK plug looks light brown, I'd be scared to run it leaner. But I will try it since you know far more than I do about these engines. The carb has a built in shim but it isn't close to being tight once I torque it down till it's at the point of stripping. So I used electrical tape as a second shim and it snugged up.

It's like the bike is sluggish and is misfiring until I get fed up and pin the darn thing for a while. Then I can pull the clutch and start off from a stop and it will pull all the way to peak rpms pretty well.

I bought the stock happy time carb and big intake manifold from revolutionarycycles on ebay for $50, jeez. Little bit steep to test the waters on, eh?