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Discussion in 'The Garage' started by Chachiboy, Jan 13, 2020 at 4:42 PM.

  1. Chachiboy

    Chachiboy XS650 Addict

    After spending weeks rewiring, I am on to the next 'to do' on my list. I never wired a motorcycle, created a electronics box and taken apart switches before so it was nice to get that under my belt.

    Next are the carbs. The previous owner had straight throug long pipes wrapped from end to end. I cut them and installed HD Sportster mufflers. Much better look and sound for me.

    First thing I noticed was kick back, sputtering and rough idle. I took the spark plugs out (see pic) and they are both black. So through some reading it seems it's rich. 5he spark plugs are 7s and not 8s so I can get that out of the way.

    I plan on searching, downloading and reading a ton (like I did with the wiring) but first off questions
    -how do I identify what carb I have and what year it is. The bike is an 81, would the carb be 81?
    -do I try adjusting air/fuel mix before jumping in too deep?
    -what's the difference between rebuild and rejet. If I have to take it out, I could essentially do it all, couldn't I?
     

    Attached Files:

    YamadudeXS650C likes this.
  2. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Your carb is a Mikuni. ;)
    Hope that helps.
    plugs SHOULD be NGK BP7ES
    Yeah those plugs are real black, you need to do basic maintenance including verifying what jets are in the carbs. But black plugs can have MANY causes.
    Carbs do look to be the correct 81 BS34
    Tells are the side pull choke and the side drain screw on the float bowl.
     

    Attached Files:

    YamadudeXS650C likes this.
  3. Chachiboy

    Chachiboy XS650 Addict

    Thanks gggGary. Do you suggest my next step is to take out the carb and inpect/the jets? Is there any type of maintenance I can do before trying to take it out
     
  4. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Last edited: Jan 13, 2020 at 7:05 PM
    YamadudeXS650C likes this.
  5. YamadudeXS650C

    YamadudeXS650C Central New York XS650 XS650.com Supporter Top Contributor

    A very smart approach.
     
    gggGary likes this.
  6. XSLeo

    XSLeo XS650 Guru Top Contributor

    www.amckayltd.com/carbguide.pdf This is a good place to start with your carbs.
    It has pics to help you determine what carbs you have.
    Once you determine that there is a chart showing what the stock jetting for those carbs is.
    There are step by step procedures for tear down, clean and inspection for the carbs. Once clean, the inspection will tell you what you need to replace.
    If careful you won't need to buy much. Gaskets are robust and if not damaged cab be reused.
    I don't know what your air filter situation is but your exhaust indicates some jetting changes may be needed.
    The pic 3G posted, is that your carbs? if so they look like the ones on my 80.
    The carb guide chart I mentioned earlier will tell you the differences between the 80 and later BS34's The side pull choke is one. Brass VS plastic floats is another.
    Once you get things inspected and determine what needs replacing you can order the parts you need. I would order some jets, One up on the pilots, one and two up on the mains.
    Reassemble the carbs per the guide. Making adjustments as you go. Things like float height, Bench sync. Just follow the guide.
    Once assembled and back on the bike you can flow the steps in the 'Tuning for Mods" section of the guide to test the carbs, Use the results of the test to determine the corrective actions needed. Make ONE adjustment at a time test, make one change, test. Repeat as needed till the carbs are right.
    Leo
     
  7. Chachiboy

    Chachiboy XS650 Addict

    Here are more pics. These are the air filters it came with. Not sure if these are stock (?) and not sure I will even keep them. Unless I twist tie them, the keep falling off
     

    Attached Files:

  8. XSLeo

    XSLeo XS650 Guru Top Contributor

    No those are not stock. with The CV type carbs you are running those pleated element pods are about the worst you can run. They cause an excess of turbulence to the air flow through the carbs. This causes a poor vacuum signal for the slide diaphrams. Thus causes slide lift issues and can be hard to tune out.
    A long straight foam filter pods is a much better option.
    Leo
     
    Raymondo and gggGary like this.
  9. Chachiboy

    Chachiboy XS650 Addict

    Good thing I was thinking to change them out! Any recommendations on what filters I should think of getting? Model numbers or names?
     
    gggGary likes this.
  10. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    grizld1, 59Tebo and Jim like this.
  11. grizld1

    grizld1 Grumpy old man Top Contributor

    Those cone filters have a flange in the mounting sleeve that blocks the air jets in the intake bell, causing a rich condition that won't tune out. Don't try jetting changes until you get better filters in place. As Gary says, with vacuum carbs you'll get the best performance from the stock still-air box.
     
    Chachiboy and gggGary like this.
  12. Chachiboy

    Chachiboy XS650 Addict


    Thanks for the advice on the filters. I will look I to the Uni filter recommendation. Although the stock is best, I have deleted my battery box for a slimmed down electronics box
     
    Team Junk and gggGary like this.
  13. Chachiboy

    Chachiboy XS650 Addict

    Are these ones any good? Or would the UNIs be the preferred choice? I notice that the suggested UNIs have foam. Better air flow? These ones have a similar filter to what I have now minus the rubber mounting.
     

    Attached Files:

    gggGary likes this.
  14. 5twins

    5twins XS650 Guru Top Contributor

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    No, those are no good either. You don't want any type of K&N style pleated filter. The pleats disrupt the air flow, make it turbulent, and these CV carbs rely on a smooth flow of air to lift the slides properly and smoothly. For your BS34 carbs, you'll want the UNI UP4229 or UP4229ST (dual layer).
     
    gggGary likes this.
  15. arcticXS

    arcticXS XS650 Junkie

    Grizld,
    What about UNI or K&N on an extension/ velocity stack 50-100 mm long?
    Surely, that would help with achieving a smooth/ non-turbulent air flow?
     
    gggGary likes this.
  16. 5twins

    5twins XS650 Guru Top Contributor

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    I started out using genuine K&N pods because, well, I had always used them in the past. But what I didn't realize or take into account was that I had never put them on CV carbs before, always just on normal slide carbs. I didn't know about the air flow issues they created. I did try them on extensions but it didn't help. Switching to UNIs fixed it.
     

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