not really.. it's something about fluid (exhaust in this case)
that i don't fully understand myself either, should have paid more
attn during physics lecture during my JC days.. hahaha.. the thing
is, having an optimally shaped (exhaust companies like arrow spend
big money on R&D just to get the right shape) belly allows the
"exhaust wave" to charge up the cylinder.
in a sense, the exhaust gases do not re-enter the cylinder via the
exhaust port, but rather, it forms a "wall" that fresh air/fuel
collides with right at the exhaust port, hence most of it stays
inside. but most of the time, a little air/fuel leaks out before
the port is closed by the movement of the piston, this is called
"scavenging". which is why 2 stroke motorcycles are banned in some
countries, and are always the target of environmentalists.
but this is the beauty of the design of a 2 stroke engine.
simplicity in design, no cumbersome and heavy cam chains, valves,
lifter arms etc.. high power-to-weight ratio. the scavenging
property is something that the most intelligent and creative
engineers cannot fix... so it's natural lah.. but honda has come up
with a 2 stroke engine called EXP-2, that uses pre-detonation to
achieve complete combustion, coupled with their "post-cylinder"
combustion thingy, it's a promising 2 stroke engine that
environmentalists won't kaopeh about. tested and proven on an
enduro scrambler, won a race.. but dunno what happened to the
design.. they're not using it leh... 
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rock hard... ride free...
