I have an MDS 40 that was giving me problems at the beginning too. Problems include: not starting, fuel spitting out carb, runs at idle but not at full throttle, and many others quirks.

What I did to get it running (still not quite broken in yet), were the following:
- 0% nitro
- idle bar plug, the Fox Idle bar plug is cheap and works great with this engine
- adjust the low end first (most people don't recommend this, but for some reason it helped my engine) for a reliable idle, since I couldn't get it to run past 1/2 throttle at first. Once the idle was reliable, I ran it at 1/2 throttle and below for 2 tanks. After this, I adjusted the high end and it is running fine now.
- 9x6 APC prop. I started with a 10x6 and it wouldn't run reliably. Once the 9x6 went on, it ran great.

I'm still running it on the bench (about 6 tanks through it now), and will continue to do this for another 4 tanks before I install this engine in a SPAD.

Good luck.

Fly NB