Just a couple of comments from someone that owns a CRRC 40. If you use the choke for a routine shut down device, it will flood the engine and make it hard to restart. Replace the Chinese plug with an NGK BPMR6F plug. My original ignition was very weak and it did not run well. I replaced it with a RCexel conversion and it runs much better and idles better. My engine needed quite a bit of break in time before it starting performing satisfactorily. Don't give up on it, I put quite a few boring break in flights on mine, and now it idles and revs up pretty well and the top end is getting fairly decent spinning a 19X8 Xoar. Good luck.
http://www.agaperacingandhobby.com/v...?productid=223
This is the conversion module for the CRRC 40 if you are interested.