If you can feel air shooting out from the head against your leg while you are riding then you definitely have an air leak. The engine will run but it will have no power because the compression is leaking out. If the leak is big enough the engine won't even run. I've seen these cheap Chinese steel heads become warped from the heat. If you have a leak you should first make sure that your head nuts are torqued to about 15 foot pounds. Vibrations can loosen them and cause a leak. If the head is actually warped I would recommend getting a high compression head with large cooling fins, they really help your engine run cooler but if you don't have the cash you can replace the stock head for under $10---->
https://www.ebay.com/itm/47mm-Cylin...920844?hash=item25e281654c:g:LDoAAOSw7ylZ5Apl Or you can try to fix it by sanding it flat with sandpaper and piece of glass method if you don't have access to a machine shop, and seeing if you can get it to seal. Other things you can do is try another head gasket, and try it, I guess, but if the head is not flat against the cylinder it won't make a difference.