Current (2011) Stihl mid-range saws, new cleaner burning engines

[KenneSaw]

I was glancing at the current Stihl lineup and noticed a couple of things.

1) they still make the MS290 Farm Boss, which lists for $110 less than the new MS291 and $70 less than the new Wood Boss MS271. Is this because it is older tech? It still weights 13 lbs as does my '99 vintage 029S. I am wondering if the old best selling MS290 is being held out as one of the last models to be eventually replaced with new cleaner engine technology models. I assume the MS291 is the future Farm Boss.

2) Comparing the MS271 to the MS291, I see the saws appear similar except the 291 has more cc and more HP than the MS271. That said, I am curious as to why the MS 291 is a touch lighter (12.1 lbs vs 12.3 lbs) than the smaller cc MS271. Both are new reduced emission engines and appear otherwise identically equipped.

3) does anyone have any technical info on Stihl's reduced emission engines and how they have achieved these reductions while keeping weight, power, and durability in mind?
Update - I found some interesting info by googleing "Stihl 2-mix". There is some animation posted on youtube of the new engine cycle.

 

[KenneSaw]

Another interesting thing I just picked up on by reviewing the 2011 Stihl catalog - they draw no attention to distinguishing between 2-stroke (conventional or lower emission 2-mix) vs 4 stroke (4-mix) engines.

I assume/guess their current backpack blowers, at least some, are "4-mix" style 4 stroke engines. Whereas of course the new lower emission chainsaws and trimmers would be new tech (2-mix) 2 cycle designs.