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Spark plug question

Discussion in 'The Garage' started by Denis Normandeau, Oct 14, 2020.

  1. Denis Normandeau

    Denis Normandeau XS400 Member

    Ok guys, while bike was idling, I pulled the left spark plug cap off. Bikes rpm went down a little bit... put it back on, back to normal.
    Then I pulled the right spark plug cap off, bike died...

    Does this mean I’m running mainly on one spark plug?
     
  2. amc49

    amc49 XS400 Addict

    Likely yes. You should be able to tell it in the idle quality.
     
  3. Denis Normandeau

    Denis Normandeau XS400 Member

    Dang, any suggestions on what I should do?
    Plugs are new from beginning of the season...
     
  4. amc49

    amc49 XS400 Addict

    Pull the plugs and compare them. What does the 'bad' one look like?
     
  5. Denis Normandeau

    Denis Normandeau XS400 Member

    Thanks for helping with this!
    Pulled the plugs, here is the left side.
     

    Attached Files:

  6. Denis Normandeau

    Denis Normandeau XS400 Member

    Right side
     

    Attached Files:

  7. amc49

    amc49 XS400 Addict

    What plug gap are you running there, it looks mighty wide but the pic angle messes that view up. Too wide a gap can kill spark.
     
  8. amc49

    amc49 XS400 Addict

    OEM gap is .6-.7 mm. Small bike coils are not well known for accepting going over OEM gap very far, set it to .6 with the problem you have now, it may help.
     
  9. Denis Normandeau

    Denis Normandeau XS400 Member

    Going to try that hopefully tomorrow and keep you posted, again thanks for the help!
     
  10. Denis Normandeau

    Denis Normandeau XS400 Member

    Re-gaped to .6mm, same problem.
    Drove to the mechanic and as he was checking, he got a shock off the left side. Suggested we start by changing the spark plug caps and then work from there... we have ordered them and should know if it helps next week.
     
  11. xschris

    xschris a lifestyle not a trend Top Contributor

    If your still using the iridium plugs make sure to use non-resistor caps.
     
    Denis Normandeau likes this.
  12. Denis Normandeau

    Denis Normandeau XS400 Member

    Ordered the non resistor caps, thanks!
     
  13. amc49

    amc49 XS400 Addict

    While getting a shock can mean plug wires or other are bad it does not necessarily guarantee such, you can get shocked with brand new components.

    And if the previously used plug was simply regapped to smaller it will still not fire, fouled plugs do not miraculously cure themselves in most cases. New plug. Once the foul short down the porcelain has been established it pretty much stays that way until destroyed by glassbeading or the like. Electricity always takes the easiest way, it will not go down the long road once the shorter one is present.
     

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