RFI problem with IS engine

HI All,

   some help please.

I have a Composite (Sting S4) with 912is Sport over 900 mostly trouble free hours.

I am planning a few more flights "Oceanic" in the Pacific and as such need HF radio. I have joined the Ham club and modified a Yeasu FT-891 for the Aircraft with a "trailing wire" antenna. This works very well on the ground.....

However in the Air there is severe RFI interference, I have tracked two sources of this (Garmin G3X and Prop controller) I can turn these off to do the HF radio calls.

But there is still some RFI coming from the engine into the antenna. When I turn off everything the RFI continues until the Prop stops turning, then it goes away.

Naturally I do not like the ides of turning my plane into a glider each time I need to do a radio call. I was trying to think of what still runs with everything off, the only thing I could think of was Stator/Regulator etc so as a test I disconnected these but still the RFI is there so long as the engine turns

I am open to suggestions !!

Thanks

Glenn