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Finding my standard...

Discussion in 'The Garage' started by willis, Feb 8, 2018.

  1. 5twins

    5twins XS650 Guru Top Contributor

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    What you have to realize and take into account when tuning carbs is that the three circuits in there overlap slightly. Changing one influences the one or ones next to it as well. In the case of the needle (midrange), a change will affect the lower part of the main as well as the upper part of the idle circuit .....

    [​IMG]
     
    SomervilleXS650 and jetmechmarty like this.
  2. willis

    willis xsive compulsive disorder XS650.com Supporter Top Contributor

    ok, pulled the other bowl and stamped sizes are the same. The left carb jets look newer and in better shape.
    Comparison pics.. Blue / Left Carb - Red / Right Carb
    0EC0A3D9-0EAA-4AF6-A7AC-C6F967AC7B9C.jpeg CF4FE16D-D42C-4AE8-9CA6-0DF8D2BE6E31.jpeg

    Sounds like I should just start fresh and order a handful of brand new pilots and mains. Any suggestion on a good place to source them? I see Niche Cycle Supply offers them at around $4 each :umm:
     
    Paul Sutton likes this.
  3. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    No pics in your post.
    Niche is my go to for jets.
    I can't help on the mains, but I've got 2 almost new #45 pilots. Yours for the cost of a stamp? PM me if you want 'em.

    IMG_20200930_132730.jpg
     
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  4. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, Niche Cycle is a good place. Make sure you get the genuine Mikuni jets because I think they sell knock-offs as well. I usually buy them in 4 packs because I'm always doing some carb fooling, but in your case that won't work out. Your '75 and '78 models use different sizes and different types of pilots.

    As you'll discover, Mikuni makes quite a few different styles of main jet. Your BS38s use the N102/221 type, nicknamed a "small round" main .....

    [​IMG]

    http://www.nichecycle.com/ncs/categ...ets/n102-221-n102-221-main-jet-by-mikuni.html
     
    Last edited: Sep 30, 2020
  5. 5twins

    5twins XS650 Guru Top Contributor

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    Here's a brand new 125 and 145 compared side to side. It's pretty easy to see the size difference with the naked eye .....

    [​IMG]

    [​IMG]

    And this shot, even though it's a bit blurry, nicely illustrates the smooth sides of the orifice hole .....

    [​IMG]

    It is still hard to determine whether your 125 is enlarged or differently sized. But, if it hasn't been altered, it's the wrong size anyway. Stock size is a 127.5, and with your freer flowing exhaust that may not even be big enough.
     
  6. willis

    willis xsive compulsive disorder XS650.com Supporter Top Contributor

    New jets are already on the way. Even if that’s not the issue then at least I know what’s in there for tuning purposes.
     
  7. Machine

    Machine Race the wind Top Contributor

    Can anybody provide accurate Mikuni "short round" style main jet thru diameters using gage pins or drill stems? Or a chart. 137.5 for example would be helpful on 78-79 BS38'S.
    Thx, -R
     
    gggGary and Paul Sutton like this.
  8. gggGary

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

    The website where I found this chart states mikuni jets are rated by flow testing and not hole size so all Mikuni sizes are "approximate"
    Keihin, Dynojet, Mikuni Jet Size Cross Reference
    All Hole Diameters Are in Inches
    Hole Dia”---Keihin # -- DynoJet # -- Mikuni #
    0.0350---- 92.5--------- 92----------- 86.3
    0.0360---- 95----------- 94----------- 88.1
    0.0370---- 97.5--------- 96----------- 90
    0.0380---- 100---------- 98----------- 91.9
    0.0390---- 102.5------- 100---------- 93.8
    0.0400---- 105--------- 102---------- 95.6
    0.0410---- 107.5------- 104---------- 97.5
    0.0420---- 110--------- 106---------- 99.4
    0.0430---- 112.5------- 108--------- 101.3
    0.0440---- 115--------- 110--------- 103.1
    0.0450---- 117.5------- 112--------- 105
    0.0460---- 120--------- 114--------- 106.9
    0.0470---- 122.5------- 116--------- 108.8
    0.0480---- 125--------- 118--------- 110.6
    0.0490---- 127.5------- 120--------- 112.5
    0.0500---- 130--------- 122--------- 114.4
    0.0510---- 132.5------- 124--------- 116.3
    0.0520---- 135--------- 126--------- 118.1
    0.0530---- 137.5------- 128--------- 120
    0.0540---- 140--------- 130--------- 121.9
    0.0550---- 142.5------- 132--------- 123.8
    0.0560---- 145--------- 134--------- 125.6
    0.0570---- 147.5------- 136--------- 127.5
    0.0580---- 150--------- 138--------- 129.4
    0.0590---- 152.5------- 140--------- 131.3
    0.0600---- 155--------- 142--------- 133.1
    0.0610---- 157.5------- 144--------- 135
    0.0620---- 160--------- 146--------- 136.9
    0.0630---- 162.5------- 148--------- 138.8
    0.0640---- 165--------- 150--------- 140.6
    0.0650---- 167.5------- 152--------- 142.5
    0.0660---- 170--------- 154--------- 144.4
    0.0670---- 172.5------- 156--------- 146.3
    0.0680---- 175--------- 158--------- 148.1
    0.0690---- 177.5------- 160--------- 150
    0.0700---- 180--------- 162--------- 151.9
    0.0710---- 182.5------- 164--------- 153.8
    0.0720---- 185--------- 166--------- 155.6
    0.0730---- 187.5------- 168--------- 1575
    0.0740---- 190--------- 170--------- 159.4
    0.0750---- 192.5------- 172--------- 161.3
    0.0760---- 195--------- 174--------- 163.1
    0.0770---- 197.5------- 176--------- 165
    0.0780---- 200--------- 178--------- 166.9
    0.0790---- 202.5------- 180--------- 168.8
    0.0800---- 205--------- 182--------- 170.6
    0.0810---- 207.5------- 184--------- 172.5
    0.0820---- 210--------- 186--------- 174.4
    0.0830---- 212.5------- 188--------- 176.3
    0.0840---- 215--------- 190--------- 178.1
    0.0850---- 217.5------- 192--------- 180
    0.0860---- 220--------- 194--------- 181.9
    0.0870---- 222.5------- 196--------- 183.7
    0.0880---- 225--------- 198--------- 185.6
    0.0890---- 227.5------- 200--------- 187.5
     
    TwoManyXS1Bs and Paul Sutton like this.
  9. Machine

    Machine Race the wind Top Contributor

    Thank you Gary. I've seen a similar or maybe even that chart on a 2manyXS1B's thread as well. I just am confused still about the 2 sets of #135's I've reamed up to .058+" over the original measured diameter of .055
    :umm:
     

    Attached Files:

    Last edited: Oct 2, 2020
    TwoManyXS1Bs and gggGary like this.
  10. gggGary

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

    Mikuni uses tapered holes to achieve flow rate, table below not accurate
    https://jetsrus.com/FAQs/FAQ_mikuni_vs_dynojet_vs_keihin_sizes.htm
     
    Machine likes this.
  11. Machine

    Machine Race the wind Top Contributor

    Oh Oh... Lol, my BS38'S main jets now have a straight bore design now then.
    Kinda like a sawed off shotgun now.
    :lmao:
     
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  12. 5twins

    5twins XS650 Guru Top Contributor

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    Yes, I could never see the point to drilling jets out. They are a precision part and not very expensive. Just buy the size you need, and buy genuine ones.
     
    Jim and jetmechmarty like this.
  13. Machine

    Machine Race the wind Top Contributor

    Most likely I will need some 137.5's again. I do have an advantage to address precision parts features as I do infact make even more precise parts than carburetor jets for a living everyday. I am able to greatly magnify and inspect items such as jets at work with modern inspection views. If those bores are tapered, it was a mistake on my part somehow to notice that? Regardless, I do expect to continue the tuning needs for sure in the future. Everybody should know my local parts sourcing habits which have been hugely affected in the Pacific Northwest by the Covid shutdown.
    One more mention is all the fraud occurring with online purchasing. In the past 3 months I have had my credit card used fraudulently twice and then canceled. My PayPal was used last week in Texas in attempt to purchase a few flashlights lol.. I have canceled my PayPal, Ebay etc. Have gone as simple online as possible out of frustration. This site is the only online membership I even remain on.
    On the upside, I continue to have very nice experiences with XS.com members in regards to parts sharing :)
    I have many times sent XS parts all over the US and even Canada and have Never been disappointed by a fellow motorcyclist!
    Long live our honesty and helpfulness to each other with XS parts and camaraderie.
    Hope to test this carb set soon.
    -R
     

    Attached Files:

    Last edited: Oct 3, 2020
    TwoManyXS1Bs, gggGary and Paul Sutton like this.
  14. Machine

    Machine Race the wind Top Contributor

    Couldn't take waiting to test the BS38'S any longer. Bike started first kick and ran thru 3 gears so nicely :)
    20201003_170052.jpg
     
  15. willis

    willis xsive compulsive disorder XS650.com Supporter Top Contributor

    New jets arrived today. A big thanks to Jim for the #45’s he sent me in the mail. Also ordered some 130 and 132.5 mains from Niche Cycle for about $4each. I’ve been doing a lot of thread reading on jetting lately hoping to gain a better understanding of what the hell I’m trying to do. First off I decided to take some pictures to document and I go so I can refer back if needed. As stated, carbs are very clean. Previously vapor blasted by OkdSkoolCarbs.
    D6FB5BAF-0AD0-4746-8541-ABA5BA38108B.jpeg

    New jets going in. 45 pilot, 130 mains. Needle clip is in slot 4 which is factory setting. New diaphragms replaced last winter too. I checked my needle jet and it was a little loose. I was able to remove it with a light wiggle. While it looks clean, I cannot get it to seat back in securely. How tight does this need to be? Is there a trick to getting some stiction in there? Do I need to worry about replacing the o-ring?
    4F5FCA47-FA28-4C46-AEFE-8EF1F13090FE.jpeg 2FAE45B5-7AE6-4CDA-A0C7-745A853EA17B.jpeg

    Fortunately I do have spare carb parts if needed. Including needles and needle jets, as I understand there are no replacement needle jets offered for 74/75 bs38’s.
     
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  16. gggGary

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

    The float bowl lip clamps it in place. a new oring will make that a tight hold. or I spose a BIT of loctite wouldn't hurt anything.
     
    Jim likes this.
  17. willis

    willis xsive compulsive disorder XS650.com Supporter Top Contributor

    Today I got a new set of grips in the mail. I specifically chose these Biltwell KungFu grips because I needs to cut the ends out to mount my new bar end mirrors and these grips looked to fit the bill for me. I’m pretty disappointed though as I figured out after I cut and mounted the left grip and mirror that they sent me two left grips. There is no way the right grip will fit over the throttle sleeve. I ordered these through Revzilla, but I’m unsure how they will respond to my email complaint since I already cut the left grip end. WTF?
    53AC72A3-E97A-4AC6-9E36-A99B6150F14A.jpeg 4D8507B0-61C4-4C34-AD08-A939D0D64C96.jpeg 14BBAF5A-6A25-42F7-B5A5-8DE284CC1680.jpeg 72BC19E4-A53C-437D-9FB0-EF2CE1A48CC9.jpeg
     
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  18. Mailman

    Mailman Hardly a Guru Top Contributor

    Well shoot, that’s a shame, and a hassle.
     
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  19. Machine

    Machine Race the wind Top Contributor

    ATV grips by chance ? :umm:
    Two lefts do not make a right :)
     
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  20. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    ....but 2 Wrights made an airplane.:whistle:
     
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