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Carb Mount Advice

Discussion in 'The Garage' started by BigMacDouble, Jan 17, 2021.

  1. BigMacDouble

    BigMacDouble XS400 Enthusiast

    I’m having an issue getting the carbs to fit on my engine . I have two that came with the kit I bought . One is too narrow to fit on the boots and the other is too wide . Is there a standard for this ?

    I tried them with both throttle bars but mixing and matching them won’t works either .

    Is it better to order a properly sized throttle bar or maybe get long boots that flange outwards ? I think I read somewhere that if you switch from air box to pod filters you’ll need a bigger gap between carb and engine so there air fuel mix has less velocity .

    Any advice appreciated.
     

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  2. xschris

    xschris a lifestyle not a trend Top Contributor

    If you have a sohc bike those carbs are for a dohc bike. You need the intake boot for a sohc bike and the carb brackets to change the spacing to make those fit. You would also need the needle jets and slide needles for a set of sohc carbs to make them work. I have never tried to make a set fit but I think a member named drewpy did this some time ago. Post some more pics of those you have. They look like dohc ones to me.
     
  3. BigMacDouble

    BigMacDouble XS400 Enthusiast

    How can you tell the differnece between sohc carbs and dohc carbs
     
  4. BigMacDouble

    BigMacDouble XS400 Enthusiast

    These are the two carbs I have
     

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  5. xschris

    xschris a lifestyle not a trend Top Contributor

    The one with the butterfly shafts out are 76-77 xs650 bs38 carbs. The others now that I can get a better look I think are 80-84 xs650 bs34. The xs400 ones for the bs34's should have two cross over barbs to attach a hose for fuel. The xs650 ones use a removable "T" fitting in the middle. Your going to have issues with so many miss matched parts.
    DSC03923.JPG DSC03924.JPG DSC03925.JPG DSC03926.JPG These are the 80-82 sohc xs400 carbs.
     
  6. BigMacDouble

    BigMacDouble XS400 Enthusiast

    I have some parts for a 650. If I get the ones on the right fully built could i not use them since theyre dohc?
     
  7. xschris

    xschris a lifestyle not a trend Top Contributor

    None are dohc carbs. But again spacing and incorrect hardware and internal components will make them very hard to use on a sohc xs400.
     
  8. amc49

    amc49 XS400 Addict

    Mainly the pressed in parts like the air jets are going to be trouble if they are not matched to fuel jets, you can really get into a mess on what at first glance appear to be carbs that will work perfectly.

    'I think I read somewhere that if you switch from air box to pod filters you’ll need a bigger gap between carb and engine so there air fuel mix has less velocity,'

    Where do people get those myths from? Lowering velocity on CV carbs even if it is a thing would be the worst thing you can do on CVs as the slides work slower with lower air speeds. As well, you already lowered it somewhat by dumping the OEM airbox. If you have to apply 'fixes' when removing the box then why would one apply a fix on top of another fix?

    Counter-intuitive if you ask me.
     
  9. BigMacDouble

    BigMacDouble XS400 Enthusiast

    I dont have the stock airbox , figured pod filters would be the cheapest option since im on a bit of a budget. Can i make the swap and then just tune them ?

    The carbs are complete i just have them apart for full cleaning. Can i just get boots that flange outwards then for either the narrow or wide ones? Like pic related
     

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  10. amc49

    amc49 XS400 Addict

    'Can i make the swap and then just tune them ?'

    Yours and do as you will. Join the thousands that self create problems. CVs do NOT like individual filters but it is a twin not a four so not as much trouble, but that is not saying you will be able to overcome it.

    Not my intention to be mean at all but it sure seems you are asking for trouble. I could as well be full of it and you 'do fine' thinking bike is running great when it is down maybe half power, there are plenty of people running around that think they are on bullets instead of turtles.

    FYI, using angled manifolds just cost you more power, you have none to throwaway there to begin with. Sounds to me like you are doing everything to turn a 40 hp. engine into a 30.

    There is no rule against that of course.
     
  11. BigMacDouble

    BigMacDouble XS400 Enthusiast

    So the solution would be to buy stock carbs and airbox? Nothing i could do with what i have?
     
  12. amc49

    amc49 XS400 Addict

    There's always something to be done but whether or not it is constructive is another thing. We make things as hard or as easy on ourselves as we do. The problem with the answer to the posed question is that the outcome will be based on the skills there and so far, putting together a hodgepodge of parts does not bode well for an excellent outcome.

    It's always best to start out with pure OEM as it provides a baseline of where you are at, then you go to changing things. if you begin with everything already changed you have no idea of which way to go as you never even had it running to begin with.

    Does that mean that I personally am afraid of anything non-stock? Not even, I've changed so many things you won't believe it but you get a feel for what will likely work vs. what won't and many cannot grasp that.

    One rock solid rule is the CV carbs will almost always run best exactly in OEM configurations. I've broken that rule a few times but you don't go just willy-nilly doing it, there is a cost doing that. If you don't believe it then go looking for CV carb mods and prepare to be disappointed, there are virtually none as compared to direct lift carb types which number in the hundreds.
     

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