Interpreting the Old Spark Plugs

F4RM@11 · Sep 22, 2012

I picked up some new Autolite 3116's today and replaced the old ones. The old ones were 386's and gapped inconsistently at .030+. While I'm not going to be diving into heavy engine work until at least next year, I am curious about what the condition of the plugs indicates about the engine.

I've posted some photos here and would love to hear what the experts have to say:

http://farmhacker.wordpress.com/2012/09/23/interpreting-the-old-spark-plugs/

Janicholson · Sep 22, 2012

They look pretty good to me. I would look for a possible intake manifold leak on the grey plug (second from right). Jim

JRSutton · Sep 23, 2012

I wouldn't call myself an expert - but from my experience I'd say they're just fine.

Looks like some soot buildup from running a little rich - but assuming they're out of an old tractor, probably where you want to be.

Hard to tune for every use, old carbs just aren't fancy enough, settings are a compromise. What's rich while riding it in a parade might be just right for plowing, etc.

No matter what the use, you're almost always better to leave it a little richer than lean.

F4RM@11 · Sep 23, 2012

Thanks for the good news.

Denny ('60 Lo-Boy) · Sep 23, 2012

I'd regap them to .023" and give them another try.

Interpreting the Old Spark Plugs

F4RM@11

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Janicholson

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JRSutton

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F4RM@11

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Denny ('60 Lo-Boy)

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