Hi kokoflyer,
1. The stock updated carburettor is probably fine, but I want to try the smaller WA-80 to see how the engine runs. In some cases, engines run smoother, are easier to adjust and handle large props better with a smaller carburettor. The most obvious disadvantage is that max rpm may be lower. To me, a smoother running engine more than outweighs the loss of rpm. In my opinion, most engine manufacturers put huge carburettors on their engines. A 10 mm carburettor on a 10 cc engine is (again IMO) much bigger than the engine needs, particularly the RCGF 10cc which seems to be built for larger props and relatively low max rpm. I used the WA-80 on my MVVS 26cc a while ago, and I only lost 400 rpm with the 7.14 mm WA-80 compared to the standard 9.53 mm carburettor. The first series of the MVVS 26cc was sold with the WA-80. Some engines seem to work well with large carburettors and use 11 to 13 mm carburettors on 26cc engines. Others "drown" when you hit the throttle. Summed up: My personal (although very limited) experience with using smaller carbs on petrol and glow engines indicates that a smaller carburettor usually makes the engine more user-friendly, but with a small loss of rpm.
2. My engine came with the first generation carburettor (rotary), which has a completely different carburettor mount than the Walbro-style engines. If you have a newer RCGF 10cc with the Walbro-style carburettor, you do not have to replace the backplate. All Walbro WT and WA (and clones) carburettors, except the really big ones, will fit without modifications.
Hope this helps!
