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idle question

Discussion in 'The Garage' started by sandmanred, Jun 14, 2019.

  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

    How long of a ride was that?
     
  10. sandmanred

    sandmanred XS400 Addict

    At least 40 miles in 10-20 mile pieces since the last change.
     
  11. xschris

    xschris a lifestyle not a trend Top Contributor

    Might be a bit lean on the left pilot and a little less on the right. I can't see the bottom of the porcelain so can't tell if you main is lean.
     
  12. sandmanred

    sandmanred XS400 Addict

    It shows on the headers a bit too. Left header has a bit more blue than the right. I think I go in with the air screw to go richer? Like a 1/2 turn or so?
     
  13. xschris

    xschris a lifestyle not a trend Top Contributor

    If your getting blue on a double wall pipe your running very hot. Might want to get a I.R. gun and check head temps. On the exhaust side of the spark plug you should see around 265-285 F That's after a 50 mile run on a 85* day. My stock bikes all have this and I have tuned my modified one to also get this.
     
  14. sandmanred

    sandmanred XS400 Addict

    I have an IR gun and made a quick check after a short run. I turned in the air screw on the left about 1/2 turn before the run. I aimed just above the exhaust at the head. It was about 260F on the left and 250F on the right though it seems to vary depending on where you aim. It was just starting to rain so my run got cut short but I will do it again after a longer run. Do you have specific spot for me to aim?

    I also checked the header at the most forward spot sitting at idle after the run and measured about 160F each left and right.
     
  15. xschris

    xschris a lifestyle not a trend Top Contributor

    In is leaner for the pilot mix screws. This is where I shoot.
    DSC03684.JPG
     
  16. sandmanred

    sandmanred XS400 Addict

    Thanks! And thanks for the correction on the screw direction too. Now I just need the rain to quit :)
     
  17. sandmanred

    sandmanred XS400 Addict

    I turned the left screw out 1 turn to make up for the wrong direction adjustment and then go a 1/2 turn more. Fired up at idle and let it warm for a few minutes. Shot in the specified spot on both sides and got about 240-245F on both sides.
     
  18. sandmanred

    sandmanred XS400 Addict

    Got a longer run in today. Turned the left screw out until it starts dropping that cylinder out and then went back in 1/2 turn so it's maybe a turn out more than the right side. Still running a bit hotter on the left, like 295F vs 280F after a ride. Seems like I went as far as I can with the pilot screw, what should I try next?
     
  19. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    If youve gone past 4 turns on the mix screws, you need to get a bigger pilot. The engine should stall when you screw the pilot mix all the way in. If it stays running, pilot is too big.

    Do a plug chop and see where you are on the main jet.. might just need to richen the needle... maybe one size up on the mains.

    Needle and main will have minimal/ if any affect on idle, but you should be tuning from the top and going down.

    Get the correct main jets first, then work your way down to the pilots.
     
  20. sandmanred

    sandmanred XS400 Addict

    Thanks for the info on the screws. That indicates I'm kind of at the limit on the pilot jet as it's happiest between 3 and 4 turns out. I've been through the main and the needle. I'm two sizes up from stock on the main and one notch leaner on the needle and get good power all the way to redline at all throttle openings.

    Would a person ever run a two different pilot jets on a bike?

    There's such a big difference between the two sides, left cylinder running much hotter than the right.

    I think I will go through at least the left carb and make sure there's nothing plugging the pilot before I go any further.
     

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