S50 Z3M firing on five cylinders

[Robin]

I wonder if anyone else has experienced this.
My S50 Z3M Ok for ten or twenty miles then tickover gets lumpy. Then starts firing only on 5 cylinders. Plug looks sooty. Not oily I'm pleased to say. Then I change spark plug on offending cylinder & Ok for about another 20 miles. Then the same happens again. This has happened about three times.
Smells a little rich. Have fitted new air filter to no avail.
Any thoughts?
Thanks

[Robert T]

Have you tried changing or swapping the coil pack?

Cheers R.

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[Robin]

Good point. I did try that. but didn't solve it. seems more like a mixture problem

[Robert T]

Got to be something confined to thr one cylinder, so next guess would be fuel injector.

Cheers R.

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