Reading plugs?

How do these plugs read?

  • Lean!

    Votes: 0 0.0%
  • Rich!

    Votes: 1 100.0%
  • Ideal?

    Votes: 0 0.0%
  • No d&#% clue

    Votes: 0 0.0%

  • Total voters
    1

Mjk

XS400 Member
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I have been running the bike for a week now, '78 XS400. Just put 30 miles on today and wanted to see what you all think of what these plugs might be indicating. I can't tell for the life of me whether they're running lean or ideal or what, it's just something I haven't picked up yet, and the differences in online pictures hardly help me at all. That being said, any help would be greatly appreciated!
 

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No doubt in my mind - Rich. Not horridly rich, but certainly on the rich side.

Using a bright light and a magnifying glass, look down into the plug and inspect the base of the ceramic insulator where it meets the body of the plug. Way down there is the true reading of the plug. Nowhere else. No how else.
 
Awesome, thanks for the help! Is the best option for leaning it out going to be a rejet or simply unscrewing the brass idle screws a bit?
 
Unscrewing the "idle screws" as you call them (they are called Pilot screws) will make the idle richer.

As for what your bike needs for adjustments, I'm not going to guess. Lean the idle mixture? Smaller Pilot jets? Lower the float levels (increase the measurement)? Lower the needles? Smaller Main jets? Sure, maybe all of those...

Before you go making all kinds of changes, try riding the bike more. Put a couple hundred miles on it, preferably in a couple long rides so the engine gets fully up to temp - that takes much longer than you'd think.
 
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