[SpudRider]

If you don't have water in your fuel, or varnish in your carburetor's jets, I suspect a failing CDI unit. Based upon my experience with this motorcycle, I doubt the gas tank has venting problems, but it's possible.

I strongly suggest you get a spare CDI unit as quickly as possible, even if this problem is determined to be fuel related. All the Chinese CDI units are prone to failure, and your Zong is not exempt from this generality. A spare CDI unit greatly facilitates troubleshooting problems such as this. In addition, when, not if, your CDI unit fails, you can install the spare CDI unit and keep riding. Otherwise, you will be unable to ride the bike until the very slow boat arrives from China.