Many do relate EMI to a Black Art... I worked with it for over 4 years in a testing facility, so I was able to learn quite a bit about commong problems. In this case, it appears on the surface that the EMI is from the ingnition, but the problem is how it is affecting the plane. There's two types of general RF emissions - radiated and conducted. Radiated is emitted from the device like it is a transmitter and conducted would be down a power or signal line. I'm assuming that it is radiated in this case, however not knowing the details makes that unknown. RF can even couple to long leads that act like antennas...

* Ensure that your ignition components are as far away from the radio as possible.

* Reduce any metal to metal contacts (ie throttle pusrhrod)

* Your receiver antenna should be routed away from any of the battery leads on the airplane's system.

The list goes on.... Obviously, test equipment to see what is going on is the answer but many don't have access to it. Let us know what you find out.

Michael