A question for ancient engineers or engineers who remember ancient engines...

[LowNSlow]

At idle rpm I can hear a ticking in my headset which stops when I turn the left magneto off. The engine is a Cirrus Minor II.

Do I have a wallet stretching magneto overhaul on the horizon or is it "simply" a fault on the ignition lead screening?

[stevef]

I'd go for screening. Get your leads tested by an AMO. A new one's easy enough to make up.
Well, they are on Bendix and TCM-type mags anyway.

[SeldomFixit]

Insulation break down - try a new set of leads or plug cap attachments - does it follow RPM ?

[LowNSlow]

Thanks chaps, looks like I need to get the leads and plug caps tested as advised.

SeldomFixit I'm not sure, I'll check next time I blow the dust off her and go flying!