MC is short for mixture control. There are no needle valves. Two servos are used to operate the carb. One for air and one for fuel. The two servos are coordinated through radio programming. A number of radios have a special built in mix just for this. My old 8UAP has a 5 point mix and works fine. Newer radios have more points. At each point the mixture can be adjusted. It takes some experimenting the first time to get the hang of it. Decent quality servos are needed with zero linkage slop. Use ball links at both the carb and servo ends of the pushrod.

The carb is handy since different pipe/prop/fuel/pump combos may like different mixture curves.

Webra makes one. OS had one but killed it off when they introduced the fuel injected engines. The pictures below show a Webra. I grafted the metering valve ($18) into a Tigre carb rather than buy another complete Webra carb.

Here is an article giving an overview.
http://www.centralhobbies.com/Engine...a/webrtxt.html

Crispyspa won't need this. His Jett carb and mini pipe suits his situation well as long as he stays within the tuning range of the Jett pipe. I ran my Jett equipped 2300 the other day. 9600 rpm with 15% cool power. APC 16x8 OS F plug. Very simple and easy to tune.