I did 2 things to my MDS 40 that significanly improved the performance:

1. Installed a Fox glow plug with an idle bar

2. The engine started losing power and sometimes stalled for no apparent reason, acting a shtough it had an air leak somewhere, but nothing plainly visible. Richening the fuel mixture helped very little. What I did was pull the carburetor off, cleaned the o-rings, and applied 'Green slime' to the o-rings. Green Slime is a lubricant/sealant for o-rings and it's used primarily on RC glow-powered cars. This stuff was actually located in the cars section in the hobby shop. There's probably different names for this as well.

I'll tell you what, these two things really improved the performance of my MDS 40 - better transition from idle to high throttle and overall power and performance is improved. Hope this helps.