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idle question

Discussion in 'The Garage' started by sandmanred, Jun 14, 2019 at 5:43 AM.

  1. sandmanred

    sandmanred XS400 Addict

    My 78 XS400E will idle at 2000-2500 rpm for a few secs when I come to a stop once it's warmed up and run at cruising speed. Sometimes more than a few seconds. Giving the throttle a rev will often bring it down to 1200-1500 but it also will come down on it's own. Is this normal? Anything to worry about?
     
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    Manometer carb sync, lean condition on the pilot circuit. Vacuum leak from bad butterfly shaft seals. Could be a few things.
     
  3. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Had a binding throttle cable that would cause a high idle. Drove me crazy but I got really good at sticking my hand down there and tinkering while on the road.
     
  4. sandmanred

    sandmanred XS400 Addict

    I can check the cable easy enough, will do that. Carb sync by manometer was just done. I'm 3 to 3 1/2 turns on the air screws. Not sure how to check butterfly seals but wouldn't that continuously affect idle? Should I try a larger pilot jet, I'm still stock there?
     
  5. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Throttle shaft seals will mainly affect idle and will give symptoms of (runaway high idle) running lean, may also affect syncing. This is compensated by going too large on jets. Shaft seals are largely overlooked because of the hassle getting access to them.

    I had a high idle in the beginning, bike would idle fine and when i revved it up, the idle would hang.

    Other possibilities included sticking advancer weights on the mechanical timing unit.

    New shaft seals made it perfect.
     
  6. xschris

    xschris a lifestyle not a trend Top Contributor

    Check to see what the plugs look like.
     
  7. sandmanred

    sandmanred XS400 Addict

    Here are the plugs. Left and right.

    [​IMG]
     
  8. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    I think those look OK, slightly lean perhaps. This is just about what my plugs usually look like.
     
  9. xschris

    xschris a lifestyle not a trend Top Contributor

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