Somewhere back in this thread I believe someone was asking about the amount of fuel that was wasted by a 2 cycle engine equipped with a muffler. I found some information in a California business publication of the California EPA Air Resources Board today.

It seems about 30% of each scavenging "cycle" is lost with a muffler equipped 2 cycle engine. I don't have figures yet for how much is saved when using an expansion chamber but certainly it is much better than 30%. Clearly the
expansion chamber compresses much of what would be wasted back into the combustion chamber.

You can see this information used in the report here:

Business Information: Clean Air Two-Stroke for Utility Engine Applications Demonstration, BKM

But this information may be general enough for these Chinese engines in the kits presently available.