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Carb jetting help plz

Discussion in 'Great Lakes U.S.' started by Cafe Murdock, Aug 26, 2019.

  1. I'm running 34mm mikunis with k&n pods n I'm about to put lowbrow customs mufflers on in the next few days n I could use help with jetting big jet is74.0 and small is 42.5 I no I need a bigger jet for start and idle but not sure on the rest carb jetting is kinda new to me on bike carbs n I'm still learning how mikuni carbs work any help would b great thanks
  2. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    grizld1, GLJ and peanut like this.
  3. grizld1

    grizld1 Grumpy old man Top Contributor

    There is no #74.0 in any Mikuni jet. From the size of the pilots jets I'd guess you have OE BS34 vacuum diaphragm carbs, but that's only a guess. The search utility works really well on this site and so does the Tech button: as the old Dylan song goes, "It's all been done before, it's all been written in the book...."
    GLJ likes this.
  4. Yea I figured thats wat they where does any one make a kit with different Jets n sizes n it that'll work on 34mm mikunis
  5. grizld1

    grizld1 Grumpy old man Top Contributor

    Sure, Keyster makes a kit. It's full of junk Chiwanese brass and guaranteed to make you wish you'd never touched a carburetor. 5twins did a fine job on the "Tuning for Modifications" section of the Carb Guide. Click the link, read don't skim, and order genuine Mikuni jets from Niche Cycle Supply.
    gggGary likes this.
  6. Ok so wat about carb sync useing a vacume gage
  7. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Comparing the vacuum gauge to the fluid tubes.

    1 tic mark on the vacuum gauge is 1 psi.

    If using colored water in a fluid tube, that's equal to a 28" difference in fluid levels.
    If using oil, that'll be a 37" difference.

    Just a matter of granularity. Coarse vs fine...
    gggGary likes this.
  8. Ok I've got snap on vac. Gage set from the 70 or so there good reliable gages but I've only ever used them on small blocks n that sorta stuff do I hook my Gage to the back. Barb's on intake tubes or is there a threaded vac. Tube hole sum where on 1980 mikuni BS 34mm carbs my motors got sum bad vibes n Poppin and stutter goin on and I'm hopein a good cleaning and resync with cure a bit of that
  9. TwoManyXS1Bs

    TwoManyXS1Bs BBQ Hunter Top Contributor

    Sorry, I've only worked on the early '71 unlinked carbs. I synchronize by feel, sound, experience.

    Can't quite make out the rest of your questions...
    gggGary likes this.
  10. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Use the barbs on the intakes.
  11. Yea
  12. Sorry I got confused there for a sec but yeah so do use the vac. Barb's to hook up me gages to sync.

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