The kind of secrecy you are trying to create with your post is either a bad marketing stint or just beyond reason.
My friend, I have seen pretty much inside and out of these F/2F/3F engines and aside from a few manufacturing differences e.g. forged vs. cast cranks, no. of oil/compression rings, compression ratios, difference in fly-wheels they are all pretty much the same. The only major difference in terms of aspiration being the single barrel carb on the F as opposed to the twin barrels on the 2F/3F. The thing most common to all three is that they are all gas guzzlers. . THE ONLY way to get better mileage on these while staying stock is to bump the ignition timing up a little and go down to smaller primary jetting, smaller power jetting and if you are really **** on mileage perhaps smaller secondary jetting. A step further would be to retrofit a smaller number venturi in the carb. Thats it. And all of this DOES make it a lot slower and a lot less powerful.
What 'more economy' also does is that it leans out the air fuel mixture which makes it burn hotter. What this does is that it burns out your exhaust valves, the quickest on the 3F. The timing advance resultant 'ping' also kicks the crap out of your internals and you can see holes burnt through pistons precisely because of this on google.
So my point here is, that while you may have the most economical 2F in the world giving 10km/l, its as good for your engine as it is believable.