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Newbie asking newbie carb questions.

Discussion in 'The Garage' started by Benwastyxx, Aug 17, 2019.

  1. Benwastyxx

    Benwastyxx XS650 Member

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    Wise,VA
    Hey guys, what an unbelievable source for all things XS! Thanks so much for the wealth of information I have already read on here. Now, This is my first bike with twin carbs. I have the linked BS38's on my 78 engine. It is mounted in a custom frame so no stock airbox. I'm pretty sure the PO just slapped some pods on it and sent it out the door. It came with a rebuild kit from ebay. I installed but didn't help. I just today ordered from Mikes XS a premium rebuild kit with the different jets and needles. I also ordered some unipods for it since the consensus on the internet is that these are the best. My question is this, What has been everyone's experience with jets and needles ( which ones) that run the best with this type of filter. It idles great, cuts out past say 2 k. I don't have a tach so Im guestimating. I have already set the timing chain tension and did a cold valve lash setting of .002 in and .004 out. Please help haha. Thanks in advance! Also what is the best way to keep the bike from rattling apart haha, thread lock seems to work the best so far but stuff keeps falling off of it haha.
     
  2. 5twins

    5twins XS650 Guru Top Contributor

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    That "premium" rebuild kit you ordered is bogus so it seems. It will probably cause you more tuning issues than it fixes. Best course of action is to just fool around a bit with different (larger) mains and pilots, and the stock needle position. If the exhaust is changed as well (probably is), then the usual routine for the '78-'79 carb set is one or two up on the pilots, two or three up on the mains, and the needles leaned a step. Mains may need to be even bigger than mentioned depending on how open your exhaust is (maybe 3 to 4 up on the mains).
     
    gggGary and JAX71224 like this.
  3. Benwastyxx

    Benwastyxx XS650 Member

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    Wise,VA
    Hey thanks for the reply! I just saw where it had multiple pilots and needles. I assumed it was designed to fix the airflow issues that pods create. Im not sure which ones it comes with. You are correct in that the exhaust is different too. Just straights that terminate under the bike in the center. Could you steer me as to which pilots and mains I should be looking for? These things are so touchy haha. My old Super E was simple to adjust compared to these things.
     
  4. XSLeo

    XSLeo XS650 Guru Top Contributor

    I agree with 5twins on this/ Carb kits that come with more than gaskets and a float valve are a waste of effort. The other brass parts are not applicable to our carbs.
    If you have the stock needle and needle jet, use them.
    In the carb guide is a chart showing what your carbs should have for stock. Use those specs to order the jets you need. Get your jets from Jets are Us or Niche Cycle, this sellers sell genuine Mikuni jets. The price is about the same as Mike's chiwanese knock offs.
    Leo
     
    gggGary likes this.
  5. 5twins

    5twins XS650 Guru Top Contributor

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    It's best you check and record what jet sizes you have now before buying more. These bikes are so old and been through so many hands, many times the carbs have already been fooled with. But, not done correctly. These carbs usually require more than just a main jet change for mods. You usually need to change the pilots and fiddle with the needle setting too. Here's a chart I made up. If your '78 carbs haven't been messed with, you should find 27.5 pilots and 135 mains in them. But, there's also a chance you won't, lol .....

    [​IMG]
     
    lakeview likes this.
  6. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    FIRST make sure exactly WHICH carbs are on your bike! A shot looking in the intake bells will will confirm year.
    use only genuine Mikuni brass. That aftermarket stuff might as well not have markings, because flow is so unlikely to match.
    Life is short, tuning is hard enough without using crap parts.
     
    lakeview, grizld1 and Machine like this.
  7. grizld1

    grizld1 Grumpy old man Top Contributor

    Click the Tech button, find the link to the old Carb Guide, and read. You've done two tuning adjustments, and that's fine, now it's time to internalize Rule One for carb tuning: Ignition first!
     
    gggGary likes this.
  8. Benwastyxx

    Benwastyxx XS650 Member

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    Wise,VA
    Thanks for the replies everyone! It has the 502 needles third position clip. It has a pamco ignition on it ( pretty sure based on pics) I don't know if there is an adjustment on the ignition though. Ive replaced the wires with 8mm accells. The rebuild kit hasn't came yet though. It has an assortment of jets so I guess Ill just play with them. The carb has 27.5 pilots and 135 mains. According to all charts, this is stock. Im assuming both jets need to be upsized for more fuel flow. Also should I set the clip on notch higher so it opens up more? I'm slowly starting to understand these things. I'm an electrician by trade and honestly VFD's and transformers are so much easier to understand lol. Thanks so much for everyone's input!
     
    gggGary likes this.
  9. XSLeo

    XSLeo XS650 Guru Top Contributor

    On your needle the grooves for the clip are numbered from the top. If you move the clip to the next up position, #2 then you are leaning the mid range.
    Moving down to #4 richens the midrange.
    I would leave the clip where it is till you figure out the other jets.
    Leo
     
    gggGary likes this.
  10. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

  11. Benwastyxx

    Benwastyxx XS650 Member

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    Wise,VA
    ok thanks! I will leave the needle alone until I change both jets. I get just adjusting one thing at a time. Would slowing down the airflow ie, wrapping filter foam around the pods do anything? I know Im just shooting in the dark here. Please excuse these newbie questions.
     
  12. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    Pictures dagnab it!
     
  13. grizld1

    grizld1 Grumpy old man Top Contributor

    Yes your XS650E (1978) has "adjustment on the ignition." If it has the original breaker point system, it has to be adjusted for both gap and timing and may need to have the advance curve corrected. If it's aftermarket it's probably Pamco with OE mechanical advance, Pamco with electronic advance, or Boyer-Bransden, and you should strobe it anyway. Go to https://www.biker.net and download a free copy of the factory manual. For how-to on adjusting breaker point ignition and maintenance of the mechanical advance governor, use the Tech button and the search function--it works really well here.
     
    lakeview likes this.
  14. Benwastyxx

    Benwastyxx XS650 Member

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    Wise,VA
    I will get pics tomorrow, Im not near the bike. I totally understand points and condensers. My old jeep has them. It is electronic however. It has the factory mechanical advance mechanism. My unipod filters came today so hopefully the kit will be here tomorrow. Thanks a bunch again! Next post will have pics
     
    gggGary likes this.
  15. Benwastyxx

    Benwastyxx XS650 Member

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    Wise,VA
    Ok so I changed mains to 142. Pilot is 35. Needle was left alone. Cleaned all passages. Idle screw at 2.25 turns. The floats are set at 24 from gasket surface. Willnot rev past idle. Cuts out and backfires. I'm taking the carbs apart again in the morning. Any suggestions? Thanks a bunch!
     

    Attached Files:

  16. Benwastyxx

    Benwastyxx XS650 Member

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    Wise,VA
     

    Attached Files:

  17. gggGary

    gggGary Stop that! Top Contributor XS650.com Supporter

    Thanx 4 pics!
    Couple suggestions
    Remove air filters, see what happens.
    Just for grins; simplify that fuel system, set up a NO dips, no filter straight to one carb line, you can just cap the inlet on the second carb, it's not needed. See what that does.
    get an inline spark tester watch it as you attempt to rev the motor. switch to other side repeat.
    Get a timing light on it check that the spark advances smoothly between idle and, well as far as you can rev it.
     
  18. 5twins

    5twins XS650 Guru Top Contributor

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    Is your advance working as it should? Sounds like it may be stuck in the retarded position and the timing isn't advancing when you try to rev the bike up. With the larger jets you put in, it should rev up. With those larger jets, once you do get it to rev as it should, I think you may find you need to lean the needle setting a step (move the e-clip up one slot and lower the needle). That's usually what needs to be done on the '78-'79 carb set when you install larger mains.
     
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