Hello Mattb
On the european Mini was one membranecarb.
If you change it wit one carb without a membrane, you also get some burping, but a better reaction on the gaspedal a litle above stationairy revs.
The membrane works like a softener.
A register carb will give better high and low reaction, so without burping.
A double carb gives better high rev performance, but misserable low.
A double, a register or any other real bigger carb does't work on a Subaru.
Why?
There is only one hole in the head!
I have tried a registercarb (homemade) and a double one. It doesn't work.
The register did a litle on high revs and was less burping, but verry difficult in building it on the engine.
My engine is build as a streaming engine, because mostly we drive full throtle!
A big carb has not enough airspeed on low revs in combi with suddenly full throtle, so will only work on high revs, like in real racingengines.
Tuning in my eyes is: bigger ports, bigger valves, stronger springs, higher compression, special exhoust, other enginetiming, other rocker and so on.
This in combi with other safety measurements for the engine.
Remember, mine goes 8.5 and more revs.....and yours about 4000.
On mine the the music is starting at 4800!
Stationairy revs are 1.6 when warm and 2.0 when cold.
Okay, a litlebit bigger new carb, with smoothening the engineports, a KN filter on it and a better exhaust. will bring some.
But there is your revlimiter.......
Benno