from what ive seen with 2 stroke engines. you will always
loose some fuel as unburned especially when running more
exhaust timing because there is a period of time where the
exhaust port is open at the same time of induction. Thats
the same reason why recreational vehicles like jet ski, atv, are
being banned from some places just because it emits alot of
unburned gases. thats with controlled ignition.

From what ive seen alot of modders don't just add timing they
also work on the case. sleeve to redirect flow to the squish band
performance goes up and does eat up more fuel than a stock
motor But from what ive seen it will always eat up more fuel
when raising up the exhaust port. I wouldn't say that the engines
are inefficient because the extra consumption is going to additional power. As long as my motors have power and makes
5 min. its all good.