Yea I know, all the smug answers like use FAI fuel and your problems will go away. This is a tough engine to get right. I have four MDS engines and the first three were perfect. The fourth is a stinker. Try using Dub Jett's way of adjusting, it helped me.
http://www.jettengineering.com/tech/techcarb.html
I found my 40 to be very difficult. It seems to need a special plug. I'm using a Fox Miracle Plug. It is happy only in a very narrow range of needle settings and the idle setting greatly affects the main needle and vice-versa. I am also using 5% Omega fuel because FAI is not obtainable here. All and all this is a tough case. I have mine running but the top rpm isn't very high ( 11,500) and the low isn't very low ( 5,500).

Perhaps I can get a hot two cycle plug (OS A3) soon and see what that does. This engine does very differently with different plugs. The Fox plug isn't the highest in rpm but seems to keep the engine running.