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1975 xs650b fuel/air mix screw setting?

Discussion in 'The Garage' started by Buckminster, Jun 22, 2013.

  1. Christen

    Christen XS650 Member

    Very nice display 5twins. Thanks
     
  2. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    Man what state are you in??? I need to fly you down to Florida to do all my adjustments on my 75!! All of this shit is foreign language!
     
  3. 5twins

    5twins XS650 Guru Top Contributor

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    This bike is a very good teacher, lol. I knew some carb stuff but learned much more dealing with the 650. The importance of knowing the year of your carb set and what size jets and needles should be in it can't be stressed enough.
     
    Raymondo likes this.
  4. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    My bike is a 75 and I believe everything is bone stock. Would these pictures be able to tell you what size carb this is?? I would really appreciate it
     

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  5. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    Also I still have the stock air cages in there. I pulled all the deteriorated foam off and fitted the green unifoam. Do you think that’s more restrictive or less restrictive? I’m scared I’m running to lean and I have no idea what I’m looking for.
    I don’t feel like doing a plug chop and I just replace plugs yesterday so pulling them out right now would not really show me anything. I get zero smoke from the exhaust and the bike turns over with the first kick.
     
  6. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    I just pulled the plugs that have been in bike for about 30 miles. Left side is left cylinder and right side is right. Notice the right side looks a lot cleaner than the left. What is all this look like to you?
     

    Attached Files:

    Raymondo likes this.
  7. 5twins

    5twins XS650 Guru Top Contributor

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    Your plugs look pretty good but you're right, 30 miles isn't much time to show color in. But still, if your carb settings were really off, it would show, and yours appear pretty good. The slight difference in coloring can probably be attributed to minor adjustments or sync slightly off.

    You appear to have the stock carbs which would be the BS38s. Here's a chart showing the stock jetting used in the different sets over the years. Eventually, if you ever take the float bowls off, you can check and verify your jet sizes .....

    [​IMG]

    Of note for your carb set is the needle setting. Notice the "-4" after your needle number (4N8) in the chart. This indicates the stock setting was having the e-clip in the #4 slot (from the top). Needles usually have 5 clip slots and the middle #3 slot is what most carbs are run at. Yours is different.

    [​IMG]

    The #4 slot yours is speced to run in is a richer setting than the usual #3 slot. So, if someone with general carb knowledge was in there, they may have set your needles in the #3 slot if they didn't have access to your carb set's factory specs. That would have the bike running leaner than it should so it's something you should probably check.

    The UNI foam wrap should flow just as well, if not better, than the original stuff, but I don't think it will flow too much to the point of needing to change jetting. Also, in your favor is the fact that the older carb sets like yours came set up richer from the factory than the later E.P.A. mandated sets. You can often get away with some minor modding without needing carb jet changes.
     
    Raymondo and Hightower-Ash98 like this.
  8. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    Man you’re awesome!! Thanks
     
    Raymondo likes this.
  9. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    So this morning I put a brand new pair of plugs in and rode about 40 miles today. Before I rode, i richened up the right side cylinder. Both now are at about one FULL turn out from fully seated.
    Take a look at the pictures of the plugs and let me know your thoughts. Side is left cylinder and right side is right cylinder.
     

    Attached Files:

    Raymondo likes this.
  10. 5twins

    5twins XS650 Guru Top Contributor

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    Those look pretty good but let me ask you, exactly what plugs are you using here? Those look like the plain "B" type. Your '75 manual probably calls for that, a B8ES. Later models switched to a hotter #7 plug, and also the "BP" type, which has a projected tip. It's become standard practice to run this BP7ES in all models now .....

    [​IMG]

    Notice how the center electrode and porcelain hang out the bottom a bit more than on your standard "B" type plug. This is supposed to give a better and more complete burn .....

    [​IMG]

    Try a set, I think you'll like them.
     
    Raymondo likes this.
  11. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    Yeah man just the regular B8ES.
    But it’s not that. I’m having a real issue too. The tach jumps all around from like 1 1/2 to 2.
    Coming to a stop light and engaging the clutch the bike wants to shut off.
     
  12. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

     
  13. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    Hey buddy so I just took the carb off. Check out my picture. I see four small pinholes. Is this what you meant by mine being in the fourth spot from the bottom of the base???
    Also looking at that chart you sent 1975 should be only 3/4 of a turn OUT from fully seated? Is that correct??
    Also are the jets located at the bottom of the bowl? Somebody told me to unscrew these two small brass screws which I circled in red in the picture and those are the jets and pull them out. Or does the float come off and the pin come out and then that gets undone?
     

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  14. 5twins

    5twins XS650 Guru Top Contributor

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    The pilot jet for the idle circuit is the smaller brass "screw" you have circled in your second pic. The main jet is the larger hole below it but it doesn't come out this way. It has to be taken out from the bottom of the bowl. Remove the drain plug and you can unscrew the jet .....

    [​IMG]

    The needle is mounted in the slide. You'll have to take the top off the carb to get at it .....

    [​IMG]

    The top of the needle will have 5 clip slots in it with an e-clip fitted into one. Correct setting for your needle is the 4th slot down from the top .....

    [​IMG]

    The needles above have the clips fitted to the top #1 slot.
     
    Raymondo likes this.
  15. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    I couldn’t get the flat head screw out the bottom for anything to get main jet out. It wouldnt budge a mm!! I put the carb straw on the inside of the bowel and srpayed the shit outta that hole so hopefully everything came out! Would you say so!??
    Also 3/4 turn out from fully seated on the mixing screw for both sides once these babies are both cleaned?? Should i start there and see how she rins and then inspect plugs or what?
     
  16. 5twins

    5twins XS650 Guru Top Contributor

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    The recommended "spec" for your mix screw is really only a starting point. From there you're supposed to adjust it in/out and find the setting where the engine runs best, idles fastest and smoothest. Usually you'll find this best running spot within a half turn or so either way from the starting "spec".

    The drain plug on the bottom of the bowl should be a hex head bolt. There shouldn't be a problem removing it .....

    [​IMG]

    Once removed, you'll see the main jet down inside the hole. In this pic, it's already been removed .....

    [​IMG]
     
    Raymondo likes this.
  17. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    Thanks buddy that really helped. Also I took the top off and needle it is at the fourth notch down. So everything is correct with that.
     
    Last edited: May 23, 2020 at 9:35 AM
  18. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    So she still stallling. I have her 3/4 out from all the way in I also tried one half and one full turn from all the way in and same thing. She runs for like 45 seconds at 13 to 1500 RPMs and then just cuts off. So fucking frustrating. The carbs are spotless. I ripped them apart last night and use two cans of CRC cleaner.
     
  19. 5twins

    5twins XS650 Guru Top Contributor

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    Well, it's possible you have some electrical "glitches". They are often mistaken for carb problems. I know you've installed new plugs but what about your plug wires and plug caps? Are they the originals? Have you checked the caps by measuring the resistance through them, and checked for good, tight, clean connections at the plug cap and coil?
     
  20. 75XSFLORIDA

    75XSFLORIDA XS650 Enthusiast

    How do I measure the resistance thru the caps?

    What setting do I put it on and does bike ignition have to be on and/or started?
     

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