RE: MDS 48 mid-range issue
G'day
A friend of mine turned up here recently with an MDS 46 which his brother bought new but had only run a few times and never flown. We tried running it and had the same problems you are having. I just happened to have a Super Tigre GS 40 (apart from a head) so I checked to see if the carby would fit the MDS and it did. The result was a very sweet running engine and it is very easy to tune now. We were running 10% nitro because that was the only fuel I had at the time.
One possible solution.
Hope this helps a little.
Mike in Oz