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New member! New bike! New... mechanic?

Discussion in 'The Garage' started by Fortune, Jul 12, 2021.

  1. Fortune

    Fortune XS400 Member

    New xs400 owner here, my first bike! I'm a bit of a hobbyist mechanic but I've always wanted an old Yamaha, I just love older Japanese bikes. Anyways, the owner was a super nice guy who let go of this bike for $300 and a chicken sandwich (I got the guy fries too for giving me such a killer deal)
    Anyways, I'll likely be posting here quite a bit in the coming month as I try and get this bike running! It's pretty complete as far as I can tell, but again I'm not a bike guy! I dropped my 74 280z project for this thing!! No keys though, but I can work with that, I found the key code on the back of the... fork plate? Whatever.
    So one of the biggest issues I've had so far, is that I'm not entirely sure... what carb setup is on this thing! It's obviously a Mikuni, but every video or image I've seen of these bikes seems to have a totally different carburetor! (What even is a carburetor, I'm 23!) Ha. Jokes aside, I'll attach images, If anyone knows of where to look to get me sorted, that would be great! Petcock seems to work, though without the carb model (and without any dang knowledge about bikes) I have no idea what I'm doing as far as routing fuel lines etc. What do I need?
    Other than that, the thing is coming along swimmingly! I've been able to do damn near everything with the toolset that came with the thing, which is pretty fun!
    Thanks for having me, folks!
  2. JPaganel

    JPaganel XS400 Addict

    Carbs are Mikuni BS series.

    I think there were two different models of them on the submodel you have, but someone might correct me on that. Still, they were all BS series.

    BS36 should be most common, I think.

    At any rate. Why do you need to know that? Parts lookup can be done by year and model of the bike. What are you trying to do?
  3. Fortune

    Fortune XS400 Member

    Considering this bike is 40 years old, typing "stock '81 xs400 carburetor" wasn't yielding too much info, believe it or not. And all the carbs I saw in results looked completely different. I'm mostly trying to find what a fully assembled one looks like so I can compare and make sure mine is put together correctly.

    Will have to take a closer look in the morning, but "BS series" has already heralded great results and should get me going in the right direction, thanks!
  4. JPaganel

    JPaganel XS400 Addict

    Ok. Looking closely, I am about 90% sure these are not the right carbs for this bike.

    Stock throttle cable attaches in the middle between carbs. I don't even see a bracket on your setup.

    Enrichment valve/choke should be on the left. And yours seems to not even be connected to the knob.

    Also, stock carbs have a different fuel fitting. It points forward, not out.
  5. JPaganel

    JPaganel XS400 Addict

    I have the same model. Here are my carbs.

    20210713_004203.jpg 20210713_004222.jpg
  6. Fortune

    Fortune XS400 Member

    Super helpful! Thank you for the clear photos. I'll have to hit the books and see if I can find out what this carb is. The carb was in pieces when I got (save for the internals) the bike and i put it together using my minimal knowledge of carburetors. Mine is definitely missing a switch for the choke. Don't even know where to start as far as dual carbs go...

    Side note: I dig the yellow
  7. JPaganel

    JPaganel XS400 Addict

    No probs.

    I am pretty sure it's a BS series, but not from this bike.

    There are two main types of XS400 - a SOHC and a DOHC. You have a SOHC. This might be a DOHC carb. I am not as conversant with those.

    SOHC breaks down into a standard (alloys and disk brakes) and "Heritage Special" or "Special", with spokes and drums, which is what you got. Both SOHC use the same carbs, although I think there may be an early and a late version. You have a later one. So, you should have same carbs as me.

    I doubt you had the carbs split. This is kind of a special PITA because the screws that hold the butterflies on can be peened over and real hard to get out without stripping. So, I don't think you got the throttle hookup wrong. I could be out to lunch on this.

    Also, the fuel inlet is definitely not right.

    However. I think you simply have the choke/enricher knob reversed and maybe missing a bracket.

    Thanks. My bike had a real crap rattlecan paintjob which peeled all over the place when I washed it. I started making things yellow just to do something different and to keep the starter cover from rusting.
  8. JPaganel

    JPaganel XS400 Addict

    BTW. You are probably going to need to do your fork seals.

    Your dust cover is split, which probably means crap has been getting in there and the oil seal is probably no great shakes, either.
  9. Jpvg

    Jpvg XS400 Member

    Awesome and welcome to the forum.
    I have a xs400 special from 1980. My carbs were mikuni bs 34's.
    Also my first bike that I am fully taking apart and restoring.
    A couple of tips;
    1. Use the toolset if possible, they have special japanese screws on these bikes and they might be hard to find replacement for.
    2. Take photos of every removal of any part or videos. I sometimes thought I could remember the order of placement of things, I didn't...
    3. Before removing some parts try to find out if they are expensive to replace/hard to find.
    4. Try to make a good plan. What will you start on first, and try to make the project do-able for yourself.
    Obviously you don't need to follow any of these things and everyone works in their own way.
    This works for me and could have saved me some 'problems' I kinda created myself.
    Best of luck and mostly I wish you a lot of fun!
  10. JPaganel

    JPaganel XS400 Addict

    Good catch.

    Those are called JIS - Japanese Industrial Standard. They look like Philips, but aren't. And a Philips screwdriver is very likely to strip them out.

    MotionPro sells a screwdriver for that. Highly recommend you spend the money on it.

    Jpvg likes this.
  11. xschris

    xschris XS400 Guru Top Contributor

    Looks like your right carb is on the left side and the left is on the right. Those are 80-82 sohc xs400 carbs. Specifically 82 sohc. Your missing the cable holder and choke rod forks. Also choke rob is on the wrong side. Wow never seen that before.
    Gra900 likes this.
  12. Gra900

    Gra900 XS400 Addict

    Well spotted xschris, that’s a challenge to do to the carbs for sure! With 3900 miles suggest you leave the engine well alone apart from standard oil change, valves, points etc. Have you ever had it running?
  13. Fortune

    Fortune XS400 Member

    Hasn't ran since I picked it up. Carbs were off the bike and the previous owner didn't have keys. All the local keysmiths have been running me in circles to see if they have a Yamaha blank in inventory, so I figured I'd just buy my own next paycheck, with the next batch of parts and such I'll be getting.

    Bike has compression and spark, just need to do fuel lines (what the hell am I doing) and fix these nightmare carbs and I'm almost 90% sure it'll run... Will it run well? Probably not. But she'll run!

  14. Fortune

    Fortune XS400 Member

    Thank you for pointing that out! It's been a huge help in getting these put together correctly. These might as well be magic to me.
  15. Buddha

    Buddha XS400 Addict Top Contributor

    Here's a few pics of the carb orientation. It's an older bike than yours but I believe orientation hasn't changed, I could stand corrected. The idle speed adjustment could be in a different location.
    Your pics show the carbs switched from side to side.
    Hope the pics help.

    Engine side

    Air filter side, the left side fuel hose goes to the petcock.

    Some 3/4 views
  16. JPaganel

    JPaganel XS400 Addict

    I have used https://keys4urride.com/ to great success before.

    Pull a lock, find the key code, and they will cut a key from that and send it to you.
  17. RedRocket

    RedRocket XS400 Member

    Cary NC
    Do these old bikes have key codes? I bought a cheap ebay ignition switch and swapped the guts into the bikes original ignition housing. Looks like you need a new gas cap, so that new cut key wont work. I think you can even get key matched replacement gas cap and ignition sets.
    As others have stated you have Mikuni BS34 carbs. Yamaha put them on 80-82 SOHC, 82-84 DOHC and the 80-84 XS650. Between year models there were some subtle external differences, This is why yours look different from others. Yours are missing the bracket for throttle cable and choke. Buy a clean, used set from ebay and build one good working pair from the two. Get a full blown rebuild kit as well. We have all seen many a well intentioned PO turn a set of carbs into a royal dumpster fire~
  18. Fortune

    Fortune XS400 Member

    Key code Is on the underside the speedo - super hard to actually get under there and read it. Thanks for the advice, everything gathered here has been beyond helpful!
  19. Macabry

    Macabry XS400 Enthusiast

    How did you get on with the carbs in the end? ... is she running now? ...
  20. Fortune

    Fortune XS400 Member

    I did a lot of cosmetic and wiring work, but had to put off the rest for quite some time, as I'm a health worker and you can all probably imagine how things have been the past year or so.

    Until recently, that is. I've managed to find some brackets I was missing for parts like the choke rod, etc. I've managed to get the carbs closer to assembled, but not entirely there as I just don't know everything about what I have here! I've got some photos attached if anyone can tell me what I'm looking at.
    Blue, from my understanding, is where the idle mixture screws should be? However there appears to just be a brass plate in their stead (both sides)

    Red, is some sort of detent for the choke, which I would assume is some sort of ball mechanism to keep the choke in a certain position. I've read several varying threads about this, however can't exactly find what I might need to make this work, or if it's technically even necessary. I have the plates to hold the choke in, and can pull it back as well, but the spring will close itself without anything to notch it back.

    Also some assorted progress pics of of the current state of the carbs
    Also have these assorted plates - which I have no idea what they could potentially be for or if they're even for this bike hehe
    Any ideas?

    Thanks for all the help so far, folks. Finally had time to work on this thing and it feels great

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