I have a 71" CMP Spitfire that gave me fits when I first converted over to gas. I exhausted the interference info at the gas engine forums and tried it all. Then one day while running the engine and scratching my head I walked around the Spitfire and just started laying my hand on everything that even slightly vibrated. (About the entire plane running gassers).
When I got to the tailwheel I grabbed it and the glitching stopped. Long story short,,,,,, metal hubbed tailwheel vibrating against it's axle causing RF noise. Switched to a plastic hubbed tailwheel and all has been fine since. "Just another thing to check in your search."[:-]