Hi Geoff
As you have done most things and are clutching at straws check the
following:
Make sure all mic/tel leads are properly screened.
Check for earth loops ie. items earthed in more than one place. It is easy
to do this inadvertantly eg. when mounting the mic/tel sockets in a metal
box, if the box is connected to more than one screen it will create an earth
loop as all screens are already earthed at the radio/intercom. Also
connecting the radio or intercom chassis to earth in more than one place can
create an earth loop.
As this engine is relatively unusual it might be worth finding out if other
users of it have similar problems.
It sounds like the problem is associated with the ignition but have you
tried isolating the alternator/generator?
Do you get interference using a handheld? If not the problem is probably due
to the way the electrical system is wired.
If I can be of any more help coem back to me.
Regards
Nigel
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