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Finally figured out my off-idle problem (I think)

Discussion in 'XJ Technical Chat' started by stereomind, May 31, 2009.

  1. stereomind

    stereomind Active Member

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    Yesterday I was messing with the carbs on the 750, and noticed something odd.. If I sprayed the enrichment plungers with carb cleaner, it would get sucked right up past the little rubber boots. I said to myself, "self, that's probably not a good thing". So I pulled the boots up and stuffed some silicone grease under them. Guess what? That off-idle stumble I've been fighting for a few months now is completely gone.

    Here's the weird part: The plungers and plunger seats are buffed, polished and completely free of debris. As far as I can tell, the air that was getting sucked in was not going straight into the main bore, but rather into the chamber just below the diaphragm, via the passageway that supplies enrichment air.

    The symptom was like this... Once the engine got hot, if I let it idle for about 30 seconds to a minute and crack the throttle, it would stumble a bit before catching on. Now, about 180 miles later (90F+ temps), the symptoms have not returned.

    Moral of the story: Replace them damn enrichment plunger boots!
     
  2. wizard

    wizard Active Member

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    That's the first I've heard of that one, something else to worry about, Thanks. :cry:
     
  3. dpawl31

    dpawl31 Member

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    Hmm... I have not thought about that.

    My boots look ok, but... it did get around my head when I took them off that they did not seal well.

    One would assume that it would only affect it during 'enrichment' but what you are saying is it goes back IN where the enrichment air usually comes from, going back in essence, right?

    Pretty sure I hit those with the propane as well... hmm. Will have to try again.
     
  4. Polock

    Polock Well-Known Member

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    i found the same thing with this setup , but i was trying to see if my 2 o-ring solution for the throttle shaft seals was working, pulled a vacuum on the fuel inlet and the choke plunger seals leaked
    never was a problem but i thought of fitting a o-ring on the plunger shaft
     
  5. dpawl31

    dpawl31 Member

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    So is the boot supposed to make a tight seal? I didn't think it was... but I need a good look at the inside of the enrichment plunger tube to see what's in there, so I can figure out if air leaking in there would do anything.
     

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