Failing coil

[Ken4004]

Just found this spark plug tester on eBay, not sure if it’s any good but it looks like a fairly basic device so it’s probably OK.

[Bryanj]

That does not test the spark plug it test wether the coil is giving a good spark

[K2-K6]

Put a spare plug in a lead  and start it with that held to earth, will verify you've got coil output.

[Bryanj]

Better if you remove the cap and see how far the spark will jump from ht lead to head, from old memory 3-4mm is a minimum

[Ken4004]

That does not test the spark plug it test wether the coil is giving a good spark

Yes you are correct I meant to say coils , sorry for the confusion

[Athame57]

I've dug up a coil from the depths of my spares pile and fitted that, all is now fine.  While the spanners where out I put a new starter solenoid in too  as issues had started with that as well.

[McCabe-Thiele (Ted)]

I've dug up a coil from the depths of my spares pile and fitted that, all is now fine.

Could you see any visible cause on the coil you changed such as casing cracks or HT leads cracks?

[Athame57]

Could you see any visible cause on the coil you changed such as casing cracks or HT leads cracks?

I binned it without really looking for those things, the pic is of a different coil, but I did notice something else. The two rectangular protrusions ( I don't know their name) on each end I thought were solid things but are actually many leaves pressed together. When unbolted from the frame these leaves splayed and showed rust. Maybe oxidation caused the failure?