A lot of folks think about installing a 2 stroke motor into a modern 4 stroke aluminum frame and I have been wondering about this for many years. I recently had to chance to buy a 2007 KX250f frame with a mid nineties KX250 2T motor (bored out to 299cc) installed. I was also very lucky in early July to find a 2003 KX144 that is close enough to a 2007 KX250 to make a rough comparison in ergonomic "feel". Ideally, I would have preferred a '13 or newer KX chassis as that is the year when the KX frames were upgraded to more ergonomically narrow and forgiving ride characteristics.
My initial thoughts on the bike without having ridden it, yet, is that it feels more bulky across the pegs, midsection, and in the rear where the right side number plate bulges outward for the 4T exhaust cannister. It is bulkier than my '14 GG 300 and substantially more bulky than the steel framed '03 KX144. The steel framed 2007 KX 250 (2T) is listed as 214 pounds dry (97kg dry, 226 pounds wet with no gas) and the AF framed 2T weighs 238 pounds (108.2kg) with all fluids, 1 gallon of gas, FMF Turbine Core II, and Maxxis Desert IT tires). If someone is looking to drop some weight by doing this conversion, I don't think it will save you much. It is possible that it weighs more than the equivalent steel 2T frame from the same year KX. What is the advantage that I see at this time? It really looks good!! That's about all I can say before having a chance to ride it on some real trails (coming soon). If the ride quality is not there, then I won't bother to try and put a GG motor into it. For now, I will have to be content with just how good this bike looks!
Eric