I have a Magnum .60 in my biplane. I have had it for a while and it is already broken in. The problem is that the engine does not hold a very good idle and it quits when i full throttle it quikly. Then after i run it for a while the idle is to high and it wont stop. I have tuned the needle valve right and everything but i still cant figure out why it is doing this.

Check your fuel system. Make sure there are no air leaks, cracks in lines, etc.... Also make sure that your pressure side of the fuel system is not cloged(or any part of the system). If runing a fuel filter.. make sure it is clean.

Also.... setting the low end before the high end needle will do this to. If that is the case.. back out the low end needle and set the high end needle first. Once you have the top end set... then go for the low end.

You have an air leak, probably at the carb mount. In rare cases, it could be
at the rear engine cover, or the head....either from the head gasket, or from
the cylinder liner. See if there is any leakage around the head gasket area.
You can loosen the headbolts and try retorqueing them.

Dave.