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Carbs - Carburetors

Discussion in 'The Garage' started by inxs, Oct 4, 2009.

  1. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

    yes I checked ...most of the kits are rubbish to be honest.

    I'll find the part numbers and see if I can order the parts I need from a Yamaha dealership. Some I could probably get someone to make like pt #37
  2. OhioRon

    OhioRon XS650 New Member

  3. 650Greaser

    650Greaser XS650 Enthusiast

    i have a set of bs34's (stock for my 1980xs) so it is a bit of an assumption they are 34's . stock air box, vacuum petcock. stock exhaust and mufflers.

    i turned the mix screw in to find out the setting. and the left was at five. and right was at 3ish . when bottomed out the left turns in farther . ??? normal.?

    screws are on the engine side, top centre. i turned them both 2 out and im running rich . . . this will be my first carb tuning. i want to instal pods and short drag pipes, but i want to get it all running good before i start messing with factors .
  4. :thumbsup::thumbsup:
    Simply awesome diagram and schematic for thinking through problems thanks great job.
  5. Mantis

    Mantis XS650 Member

    Just 've got 1982 xs650 heritage.
    Does anybody know how to adjust the carbs? It was hard to get the mixture screws out, but it happened.
    Now I need to set them correctly.
    I am pretty sure you guys know how.
    Thank you
  6. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Page 1........first post...............first link..........

    Read through it thoroughly...............If you post questions without reading the "carb guide" then you will keep getting referred back to it.

    The carbs on an 82/83 should be BS34's
  7. Mantis

    Mantis XS650 Member

  8. schlad12345

    schlad12345 1975 stock everything

    Why does the carb. guide say that the mixture works in reverse? Is this true on carbs from a 75 all stock no mods. original carbs and does anyone have a good way to check if I'm running to lean I'm about to take a long trip and don't want to damage my engine any help would be much appreciated thanks!!!!!
  9. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor

    On stock Mikuni carbs the mixture screws do not work in reverse. Screw in CW and the mixture is lessened, screw out CCW and the mixture is increased.

    Tell everyone what exhaust you have and do you still use the stock airbox and stock type air filter? If you have open exhausts and pod filters, you will run lean unless you have rejetted the carbs.
  10. grizld1

    grizld1 Grumpy old man Top Contributor

    schlad, there are two different types of pilot mixture screw controls in common motorcycle carburetors. The type found in Mikuni BS series carburetors increases engine vacuum over the pilot jet as the screw is turned out, so that more fuel is picked up through the pilot jet and the pilot mixture is richened. As a general rule, the mixture screw will be located forward of the slide tower on carbs with this type of system. Older designs like Mikuni VM series, mechanical slide Bings, and most Amals, use a control system that adds air to the pilot mixture as the screw is turned out, leaning the mixture. As a general rule, carbs with this system have the fuel screw located behind the slide tower.
  11. Mantis

    Mantis XS650 Member

  12. brian wilmington

    brian wilmington XS650 New Member

    how do you clean the oem stock air filters that come on a bs38 mikuni carburetor on a late 70s xs650? as you know ,they have a wire cage support inside so you cant soak it in kerosene and squeeze it out.
  13. Tonyterlingua

    Tonyterlingua XS650 New Member

    I have a 76 650. I'm brand new at this site. Thanks for all the carb links. How do l know if I have CV or VM carbs ? My carb problem is this; on startup & @ idle the left cylinder runs fine but the right doesn't fire til about 2k rpm.pops a nice flame out the right pipe ! Plugs look fine. At idle with air cleaners off a mist wafts from rt cylinder. Any thoughts gratefully accepted.
  14. grizld1

    grizld1 Grumpy old man Top Contributor

    Easy. Click the link to the Carb Guide, and read it. Many versions of the BS-series vacuum carbs were used on different models of the XS650, and often carb sets from one year find their way onto a bike from another year; read the identification material carefully, as well as the carb ID material at Mike's XS. VM carbs are aftermarket items, easily identified by cables passing through carb tops to mechanically lift slides.
  15. I've read theough many of the files in the opening post, and these are my lingering q's:

    xs650se bs38 carbs

    Air mix screw: why do they say go all the way down and then turn out more? Wont that do damage to the screw tip?

    Needle jet (z2): mine fits snug but is it supposed to face any particular direction?

    Idle screw: After bench synching butterflies, I wasnt sure what setting to leave idle screw at. I read that the left screw should be screwed all the way down. But That leaves the butterfly traps slightly open... I cant see this being right as I'm sure they need to close when rider is off the throttle.
  16. 650Greaser

    650Greaser XS650 Enthusiast

    Air Mix screws: turning them in lightly won't hurt any thing. Just bottom them out so you know your at zero. And then you know how many turns out from zero you are. Count and document how many turns they are before and after for reference, they don't always match up exatly. "Every carb is its own animal"

    Needle jet points down. If it doesn't slide nice clean it better. Maybe lightly sand with <600 and polish.

    Idle screw: is ajusted when you are idling . turn it out to lower idle. I adjust mine all the time at red lights when I notice I'm idling high.

    Disclamer . I am by no means an expert . so yeah. Just a fellow bike fiddler .
  17. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

    If you initially bench sync the butterflys a good method is to blow into the carb at the butterfly end like a trumpet. You can adjust the sync screw until you feel an equal pressure when blowing into both the carbs then set both the throttles with the idle set screw.
    A good starting point is to have the butterflies almost closed so that blowing into the carbs requires quite a bit of pressure and your cheeks fill up with the back pressure. Butterflys often do not fit precisely in the venturi so using drill bits and pieces of paper etc might not necessarily give you equal air flow when bench syncing

    When the carbs are fitted you should adjust the throttle shaft idle screw to get a reasonable initial idle speed (don't touch the central sync screw setting) so that you can run the bike warm the engine up and then set the idle mixture using the air screws
  18. Thanks fellas. I guess I was stressing out for nothing. Better to ask imo :)

    Ps:bikefiddler, compared to me, you are an expert!
  19. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Last edited: Oct 10, 2015
  20. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

    ignore Skull .:D
    He won't post anything helpful to you.....I've put him on IGNORE :laugh:
    He's just here to Troll me cos he's got this thing about Pomeys :laugh::laugh:

    The advice I gave you about bench synching the carbs is good ...hope you get somewhere today.:thumbsup:

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