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Only one plug gets sooty - very quickly!

Discussion in 'XJ Technical Chat' started by UK550Maxim, Jun 2, 2014.

  1. UK550Maxim

    UK550Maxim Member

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    XJ550 Maxim: One plug is fouling up - black dry sooty. The other seem ok. This happens very quickly, within 20 seconds of start up. There is an occassional popping coming back through the carbs of that (no 1). the spark on the plug seems ok. The carbs have been cleaned and refurbished so not expecting the problem to be there but can't absolutely eliminate of course.

    Any ideas what to check?
     
    UK550Maxim, Jun 2, 2014
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  2. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Enrichment plunger not sealing off?
     
    bigfitz52, Jun 2, 2014
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  3. BruceB

    BruceB Active Member

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    BruceB, Jun 2, 2014
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  4. UK550Maxim

    UK550Maxim Member

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    Sorry guys, not sure what you mean by the enrichment plunger - (Pilot Screw?)
     
    UK550Maxim, Jun 2, 2014
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  5. UK550Maxim

    UK550Maxim Member

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    ok... I think see what you are getting at now, the 'main' plunger that has the diaphram fitted to it. If that was an issue, given that I have the pods off and can see them operating, wouldn't I see this sticking or something? They do all have a petrol varnish look to them but they all were fine in the drop test and if i push them up they come back down in the same way. Not sure what I should look for and or do to them?
     
    UK550Maxim, Jun 2, 2014
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  6. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    What I was referring to was an enrichment plunger; not the slide.

    Those plungers that the "choke" lifts up, to dump extra fuel into the carb throats. They are effectively valves, that have to close off the passage of fuel when they are not being lifted. If one of them isn't closing properly (or not sealing properly) then it would produce the same effect as having the "choke" on for that one carb only.
     
    bigfitz52, Jun 2, 2014
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  7. UK550Maxim

    UK550Maxim Member

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    Right'o...... swapped the best plunger on my donor carbs for the one on that carb and had a ride. Thought the bike seemed smoother and was convinced that had done it but on return the plug was sooted up again :(

    I did a quick wet float balance test - it was a bit rushed (table not quite as flat as I would have liked and doing it by eye, but it seemed ok and in line with the others.

    I know the coils aren't quite to spec but seemed to be ok and it is just one plug not two. I can swap the coils over though to be sure.

    From memory the compression is poor on that cylinder so wondering if that is related?
     
    UK550Maxim, Jun 2, 2014
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