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Does this make sense?

Discussion in 'The Garage' started by MikeC23, Jun 6, 2018.

  1. MikeC23

    MikeC23 XS650 Addict

    '79 special with stock pipes and uni foam air filters. I went up 1 size on my pilot and main and dropped the needle one clip (leaner). Bench synced the carbs. Bike starts up right away but idle is rough. RPMs climb even after putting a set of OEM Yamaha advance springs on. When setting the air/fuel mix screws, it runs the best with them COMPLETELY in. That is what doesn't make sense to me. I figured they would be somewhere around the recommended 2.25 turns out. Am I overlooking something? Maybe I missed an air leak somewhere?
     
  2. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    MikeC23 and robinc like this.
  3. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    Last edited: Jun 6, 2018
    JRay77 and MikeC23 like this.
  4. MikeC23

    MikeC23 XS650 Addict

    Unfortunately, no. I went and bought mikuni jets. I even checked and double checked to make sure the metering orifices were in the right place. I'm going to give those threads a read through now. Thanks, guys!
     
  5. 5twins

    5twins XS650 Guru Top Contributor

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    Your mix screws are fuel regulating, or more correctly, fuel-air mix regulating screws. Turning them in (closing them) will make the idle circuit leaner so the fact you need to close them right up seems to indicate you're too rich. An air leak would make things leaner.

    What style of UNI pods do you have, the short ones with the plastic end caps or the longer all foam ones? If you have the short capped ones you may not need to re-jet at all. We put them on a local guy's otherwise all stock '78 and didn't have to change any jets. You might try the stock jetting again, or at least the pilot, and see if that puts the mix screw setting back up where it should be.

    Another possibility is the air jet feeding the pilot circuit might be plugged. Then the pilot jet would flow just fuel and get no air to mix with it. The pilot air jet is located around the edge of the bell mouth where the pod clamps on, at about the 4 o'clock position. Air blown through it should exit out one of the angled ports on either side of the needle jet on the bottom of the carb body .....

    [​IMG]

    [​IMG]
     
    JRay77, TwoManyXS1Bs, gggGary and 2 others like this.
  6. MikeC23

    MikeC23 XS650 Addict

    They are, indeed the plastic capped ones. I'll toss the original jets in and see what happens this weekend and will check that air vent while I have the carbs off.
     
  7. MikeC23

    MikeC23 XS650 Addict

    TwoManyXS1Bs and robinc like this.
  8. MikeC23

    MikeC23 XS650 Addict

    While doing more investigating, it seems as if I have an air leak somewhere in the vicinity of the throttle shaft on the right side too. New seals are on their way!
     
    robinc and mrtwowheel like this.
  9. angus67

    angus67 Welder's penetrate deeper!!

    Were did you buy the seals from?
     
    robinc likes this.
  10. MikeC23

    MikeC23 XS650 Addict

    McMasters Carr
    2 90025K135 x-Profile Oil-Resistant Buna-N O-Ring, 1/16 Fractional Width, Dash Number 011, Packs of 100 1
     
  11. angus67

    angus67 Welder's penetrate deeper!!

    Good on you for not getting mikesxs
     
  12. MikeC23

    MikeC23 XS650 Addict

    Yeah, I read a handful of other forum posts that recommended against Mike's. I've had some really bad luck with stuff from Mike's lately. Like my timing advance springs. The ones from Mike's didn't pull the bob weights back in fast enough so I had to hunt out OEM Yamaha ones on ebay.
     
  13. gggGary

    gggGary I'm listening, change my mind XS650.com Supporter Top Contributor

    The advice to use those X seals is severely outdated. Buy oem yamaha, or suzuki also sells the CORRECT seal, which has a MUCH different profile and uses the pressure differential to improve the sealing.
     
    MikeC23 likes this.
  14. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, I came up with that substitute years back when I thought Mike's was the only source for them and they cost $5 each. They do work but I can't comment as to their longevity because I installed them in a spare carb set that only gets occasional use. I didn't realize Yamaha still made and sold the proper seal, and at a better price (about half of Mike's). Current best deal is the Suzuki part, same exact seal and about a dollar less than Yamaha .....

    https://www.partzilla.com/product/suzuki/13651-51010

    https://www.partzilla.com/product/y...?ref=0c2514270f638cfd80aa2c78e639f3d5a7971cda
     
  15. MikeC23

    MikeC23 XS650 Addict

    I'll order some of those Suzuki ones to have on hand. I slapped my carbs back together and they're on the bike, so I'll swap things out the next rainy day. Based off of the crap-ass Western Pennsylvania weather we've been having, that won't be long from now!
     
    gggGary likes this.
  16. 5twins

    5twins XS650 Guru Top Contributor

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    If you already installed the x-rings, I'd say run what you got until they crap out. Like I said, they work but I'm just not sure for how long.
     
  17. MikeC23

    MikeC23 XS650 Addict

    They worked for about a day...
     
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  18. xschris

    xschris from earth

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    I bought some x-ring types off ebay a while back for a few of my xs400 bs34 carbs and have put about 1000 miles on one set and still no leaks. The bike runs great just good as when they where new. Time will tell I guess.
     
    robinc likes this.
  19. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, even though I haven't run my spare carbs that much, they have seen longer than a day's use, probably several weeks at least so far.
     
    MikeC23 likes this.
  20. MikeC23

    MikeC23 XS650 Addict

    I was still leaking air around the inner parts of the throttle shaft. Just to be sure I'm not being a complete moron and missing something, does anyone have the order of parts for the throttle shaft assembly for 79 bs38's? Maybe I dropped a washer on the floor and overlooked it or something! Anyway, the Yamaha ones will be here tomorrow so I plan on hurrying up and getting this thing running tomorrow night. Nothing like the 11th hour. A friend of mine is hosting a Rocker's event for Thunder in the Valley and was planning on having my bike there on Friday. Looks like the neighbors are going to listen to me getting this thing running into the wee hours of the night!
     

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