On a Ryobi with mag ignition, I experienced lots of interference due to a metal throttle rod, well isolated by plastic ball links. Changine the rod to nyrod eliminated about half the glitches. Wrapping the complete HT cirquit with copper mesh and linking to engine earth eliminated the other half. All the time, radio components were at 30cm (12") from any ignition component. Same thing with Quadra om mag ignition.
The new EI units tend to make us sloppy in our thinking, because they are so well shielded. It never hurts to be on guard for those pesky high voltage radiation peaks.