RE: rearmounted carbs.
I have a DA85 and it runs fine. The carb goes through the firewall and the air is drawn in from around the inside of the motor box. The motor box itself has holes in the sides and top and bottom. I like the rear carb design from the standpoint that the engines can run the same right-side-up or upside-down. I have had several engines (DA100, 3W-100, DA170) that have carburetors hanging from the bottom of the crankcase and sometimes they run differently when they are upside down. This can be caused by fuel puddling. At low throttle settings there is not enough air flow to completely draw all the fuel into the combustion chamber. But upside-down, gravity assists and most of the fuel ends up going through the engine, richening it slightly as compared to when it was right-side-up.
The worst thing about the rear carb is sometimes it is more difficult to get at the needle valves because the firewall is in the way.