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Help...anyone?! Carb identification & general chaos...

Discussion in 'The Garage' started by Mjerrold, May 21, 2023.

  1. May 21, 2023 #1
    Mjerrold

    Mjerrold XS400 Member

    6
    10
    3
    England
    Hi guys,
    I brought an early x400 last year but never really got it running right and i'm kind of losing the will to live!

    Pic here for attention...

    Screenshot 2023-05-21 at 18.35.11.png

    The bike has never been able to start without a healthy squirt of easy start. So I know theres something wrong there. These are the carbs that its running - which to my research I dont think are factor fitted? Anyone know what they might be?

    Screenshot 2023-05-21 at 18.35.20.png

    Iv also noticed that (I assume) is the fill for prime is just wide open and will be sucking in air. Indicated here as ref 1 - am I correct? The petcock fitted on the bike doesnt have a prime.


    Screenshot 2023-05-21 at 18.34.46.png


    I would be so grateful is some XS Wizard out there could confirm my suspicions and let me know if you think its worth trying to get a petcock that will accommodate the prime on the carbs or if I should just block that up to stop the air messing with the mixture.

    A million thanks!
     
    Mjerrold, May 21, 2023
    Mjerrold, May 21, 2023
    #1
  2. May 21, 2023 #2
    CaptChrome

    CaptChrome XS400 Addict Top Contributor

    317
    103
    43
    Southern NJ
    Definitely not original carbs. #1 is probably a vent/overflow, but without knowing the exact model, that is a guess on my part. It also could be the suction for a crankcase vent.

    What sort of intake do you have (I'm guessing that the original system is long gone)?
     
    CaptChrome, May 21, 2023
    CaptChrome, May 21, 2023
    #2
  3. May 21, 2023 #3
    CaptChrome

    CaptChrome XS400 Addict Top Contributor

    317
    103
    43
    Southern NJ
    For what it is worth, these look like Suzuki GS500 carbs (Mikuni BSR-34). If this is so, then port #1 is a vent line to atmosphere, port #2 is the fuel inlet and there might also be a vacuum port on these carbs that will need to be capped off or it will cause a lot of issues.

    Oh yeah, never mind about the intake system, I can now see that it has pod filters.
     
    CaptChrome, May 21, 2023
    CaptChrome, May 21, 2023
    #3
  4. May 21, 2023 #4
    Mjerrold

    Mjerrold XS400 Member

    6
    10
    3
    England
    7A4F37EE-05C7-4BF8-87D4-9B71FD0E3111.jpeg Thank you so much for the reply. Just looking at the top of the carbs and it looks like you’re dead right. Missing a cap? Looks like one is capped and the other isn’t.

    Bike seems to run lean which I thought was a result of the open pipes but assume that vacuum would cause that? Sucking in too much air?
     
    Mjerrold, May 21, 2023
    Mjerrold, May 21, 2023
    #4
    CaptChrome likes this.
  5. May 21, 2023 #5
    CaptChrome

    CaptChrome XS400 Addict Top Contributor

    317
    103
    43
    Southern NJ
    I don't know if that is the vacuum line or not, but an open vacuum will definitely cause a lean condition. Make sure you look over the carb bodies carefully and cap anything that you are not using. Go over the intake boots, vacuum hoses to the petcock, petcock, etc and address/replace anything that looks like it might leak. Once the bike starts, I would even put my finger over the vent, just to make sure that It is not doing something unexpected to the mixture.

    Also, download a copy of the GS500 manual and it should tell you how to check/set the fuel level in the float bowl for these carbs. That will eliminate one more variable.

    One question if you know - do these fit up directly to XS400 carb holders, or is something else being used to mate these carbs to the engine? Curious minds want to know because if stock, ganged up GS500 carbs fit right up, that opens a whole new world of cheap replacement carbs for the XS400 (and the other way around also.)
     
    CaptChrome, May 21, 2023
    CaptChrome, May 21, 2023
    #5
    tstidham likes this.
  6. May 24, 2023 #6
    Mjerrold

    Mjerrold XS400 Member

    6
    10
    3
    England
    Massive thanks for the help. Ive done some digging and yes you're right they seem to be GS500 carbs.

    I've just stripped them down and cleaned them up while they were off the bike. Following some other GS guides I can see that the vent indicated in my original post is as you say: just an breather so nothing to worry about there. I also found a few images and it appears the below IS for a vacuum line and both should be blocked up when not in use.
    Screenshot 2023-05-24 at 18.08.19.png

    Before I put them on I will inspect all the rubbers, hoses and other bits to make sure its not sucking further air in there.

    In regards to if these are a simple swap for factor fitted XS carbs, I'll take some photos of the carb holders and check diameter. Other than that unfortunately I wouldn't know if it was a straight swap. From memory they seem to modified in any way.
     
    Mjerrold, May 24, 2023
    Mjerrold, May 24, 2023
    #6
    JPaganel likes this.
  7. May 26, 2023 #7
    gpounce32768

    gpounce32768 XS400 Enthusiast

    35
    15
    8
    Baltimore, MD USA
    The vent and fuel rail fittings between the carbs look original as do the mounting rails. I suppose the carbs could have the bodies milled so they fit closer together while retaining the original fittings, along with new mounting rails. I'd bet on them being in original condition- a strong family resemblance to the carbs on my old Bandit. If you find the black fitting rotten at all its easily replaced. It should have a hose run up under the seat perhaps, to get it out of the ambient airstream; protect it from rain & debris etc.
     
    gpounce32768, May 26, 2023
    gpounce32768, May 26, 2023
    #7
    tstidham likes this.
  8. May 26, 2023 #8
    tstidham

    tstidham XS400 Addict

    164
    65
    28
    Philadelphia, PA
    You could put a lawnmower type fuel filter on that vent hose to keep out debris too.
     
    tstidham, May 26, 2023
    tstidham, May 26, 2023
    #8
    gpounce32768 likes this.
  9. May 31, 2023 #9
    Mjerrold

    Mjerrold XS400 Member

    6
    10
    3
    England
    UPDATE!!

    Well, I cleaned out the carbs throughly, flushed the tank and then did the electrolysis technique to make sure it was all clean. Then I blocked up that top that vacuum line, replaced the fuel filter with a bigger one, put it all back together… first press and it burst into life! It’s never started that easy since Iv owned it. Wahoo!!

    I think I’ve done too many turns on the idle screw because it’s revving like crazy but I’ll get a stubby screwdriver and adjust them on the bike.

    Im chalking that down as a success - thanks alot guys!
     
    Mjerrold, May 31, 2023
    Mjerrold, May 31, 2023
    #9
    gpounce32768, CaptChrome and tstidham like this.

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