I have a couple of pre-Chinese ST 2300 engines.
They wouldn't run well to start with....better after I modified the carbs as per this link
http://www.rcaerobats.net/STEng/Supertigre.htm
then got them set decently, used an OS "F" plug and 15% fuel.
I have since installed a Perry pumper carb and a VP-30 pump....awesome runner now!
I have not messed with the original carbs since and I have heard that the "Chinese" carbs ars better.
Thanks
John