Unhealthy Spark Plug

Discussion in 'General Questions' started by bilboby, Aug 20, 2010.

  1. bilboby

    bilboby Member

    Sometime back a fellow MB rider posted asking for help concerning his spark plug ofwhich other members asked he post pic's of the SP in question. However i cannot find his thread so i've posted below a four pic's of a SP (active AX80) which doesn't look healthy and therefore would like some advice on the cause. MB riding is great fun but it's becoming a real pain in the *** getting the bike rear friction engine to run smoothly without the annoying teething problems.


    Attached Files:

  2. GearNut

    GearNut Active Member

    The air/ fuel ratio is too rich. That is why it is black. The center electrode is showing signs of wear, but it is not worn out yet. I see dirt in the threads of the spark plug too. Clean all of that off, as well as the seating area on the cylinder head.
    Use a little anti-seize compound on the spark plug threads to protect the threads in the cylinder head and help seal the threads from the weeping oil.

    Last note, if the engine is running very well with the current air/ fuel ratio, you can switch to the next hotter spark plug which will burn off the contaminants better.

    It would be better for the engine internals to have the extra fuel as all the lubricating oil it sees is in the fuel.
  3. kerf

    kerf Guest

    I run synthetic oil in my two stroke at 25:1. I realize this is anecdotal but while my plug may be black from a rich mixture, I get no carbon fouling. The piston and exhaust port stay clear of carbon too. I have found, especially where oil is concerned, cheaper ain't always less expensive.
  4. bilboby

    bilboby Member

    Cheers MB Comerades i've taken onboard your suggestions and will set about cleaning the plug & thread etc. Unfortunately i'm hopeless at measuring blind exactly the right oil - gas mixture thus i've been searching for a mixture bottle kit needless to say that in France upto now no joy. It appears that french motorbike shops assume we're all intelligent enough for knowing without such kit's the right oil quantity ofwhich i do but i have no means for measuring exactly. Such bottles are available in the US but the cost of shipping can be upto 3x that the cost of the item.

    Once again cheers & good MB riding
  5. GearNut

    GearNut Active Member

    Try a baby bottle. They are graduated on the sides for measuring out formula, ect.
  6. bilboby

    bilboby Member

    Hey GearNut,

    Great idea so i'll have a look on the baby shelves next time i take her indoors shopping next Saturday.

    Cheers & happy MB riding

  7. bilboby

    bilboby Member

    Is this a good way for testing SP's & it's spark as i've hit on the idea using a voltmeter between the SP & cap & whilst pull starter cord notice that high voltage of sorts is registering on the meter. Such info surely must suggest that SP's are ok & igniting?

  8. GearNut

    GearNut Active Member

    That could indicate that voltage is present, but will not show if the spark plug is actually sparking under compression in the cylinder.
  9. bilboby

    bilboby Member

    So i'm back to square 1 but many thank's anyway.

    NB: Given the lack of MB activity i'm getting due to stupid/small motor/mechanical problems from knowing nothing at the start i'm now starting to understand how such engines work. But that's only thank's too MB members on this forum who find the time to reply with helpful answer's.

    Cheers everyone