Don't go doing anything drastic until you have a gallon of fuel through your JBA. I have 3 SK engines (2 .91 & a .50) and a JBA .56, plus I broke in and flew a JBA .56 for a friend. Chinese engines do not have tolerances that are as closely controlled as an OS, and I have 2 .55s and 4 .46s. My Chinese engines have usually needed a gallon through them before they really idled well and shut down. I'd fly it until you have a gallon or a gallon and a half through the engine before I started tearing is apart looking for air leaks.

I have some GMS engines and they were the same way, took longer to break-in and wouldn't shut down for a while.

People who take any of these engines, run a tank or two through them in a slightly rich 2-cycle and claim they are broken in are just kidding themselves. It's going to take some running on the less expensive, Chinese engines.