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1981 Yamaha XS650S - Project Bike #5

Discussion in 'The Garage' started by rbirkey, Aug 3, 2019.

  1. rbirkey

    rbirkey TriumphBonneville.org

    I recently completed my first vintage Yamaha XS 650 project bike for a friend (1977 XS650D), having spent years working on Triumph Bonneville's. I learned so much on that project (with lots of great help from this forum) that I decided to buy another project bike which is #5 for me. It's a 1981 Yamaha XS650S "Special". So far, I've just started tearing it down.



    I'm not sure yet what final direction I will go on this one, but it will probably include the following:
    • Battery
    • Tires and tubes
    • New LED lighting
    • New mini gauges
    • Euro bars / grips
    • Performance mufflers
    • Airbox removed - pod filters
    • Rebuild carbs
    • New seat
    Open to your experiences, thoughts, ideas, and suggestions!
  2. 5twins

    5twins XS650 Guru Top Contributor

    Although much of what you learned working on that '77 will apply, there's lots different on this '81 model. The 2 biggies are the carbs and the ignition. There are also more "safety" features like the auto-on headlight and a clutch safety switch (kills starter if bike is in gear and clutch lever isn't pulled in).
    YamadudeXS650C and MaxPete like this.
  3. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    I recently finished an 80 Special. The threads a real slog at about a hundred pages, but you can prolly find some useful info in there since they're only a year apart.
  4. Mailman

    Mailman Hardly a Guru Top Contributor

    Well I’m so happy you decided to come back with one of your own! This ought to be fun!
    Raymond, MaxPete and Jim like this.
  5. xjwmx

    xjwmx It's just the unknown. Top Contributor

    Looks like it's in good shape to start with. Mine is an '81 too. I like the combination of cast wheels and drum rear.
    MaxPete likes this.
  6. lakeview

    lakeview XS650 Guru XS650.com Supporter Top Contributor

    Always liked that silver colour.
    Wulfbyte and MaxPete like this.
  7. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Does the bike run.............does the electrics, (TCI and associated parts) and charging system work............These things would be easier to sort out before tearing into the bike...........
  8. rbirkey

    rbirkey TriumphBonneville.org

    The bike does not run yet. I will install a new battery and clean out the carbs and fuel lines then see what it does with the current electronics. It was running last in 2002 and has approx. 8,500 miles on it.

    I do not like the stock seat on this bike. It looks bulky and heavy for the lines of the bike. I much prefer the look of the earlier XS650 seats like the 1977 model. Are there good options for using a more traditional long seat on these bikes?

    Also, I want to use some modern performance tires. I like Avon Roadriders on my Bonneville's and in another thread, someone suggested Avon Speedmasters as a good option... ?? Are these rims tubeless?


  9. Machine

    Machine Race the wind Top Contributor

    This is a Great bike to go creative with on mods ! It will be very good to watch this one :)
    That 77D was an original beauty that is just very hard to find.
    A drum brake Special to play with ? Yes, that’s a good time !
    Glad you have taken this on
    rbirkey, Mailman and MaxPete like this.
  10. MaxPete

    MaxPete Lucille, Betty, Demi & Gretel: I ask, THEY decide. XS650.com Supporter Top Contributor

    Looks like a great basis for a snazz bike Randall - well done!

    Aside from some of the obvious appearance differences, the Special will have an electronic ignition which is usually quite reliable - but we are told do NOT weld on the bike with the ignition module mounted. As mentioned, it will likely have a bunch of safety “features” as well as self-cancelling turn signals and one that wasn't mentioned: a switch on the side stand which disables the engine if you put it in gear with the stand down.

    Cheers - and lots of photos please!

    YamadudeXS650C, rbirkey and Mailman like this.
  11. rbirkey

    rbirkey TriumphBonneville.org

    I've completed more deconstruction today and can assess some of the things I will need to address.
    • The exhaust system is shot - will need to replace
    • Carbs are really bad. Corrosion beyond what I found on the 1977 XS650D. I may need to replace/upgrade these as one pilot jet head is stripped and stuck in its passage!
    • Ignition and electrical components look to be in good shape.
    • The cam chain tension was way off! I've corrected it.
    • Rear brake looks pretty good
    • spark plugs are pretty black with carbon... must have been running rich
    • Will probably replace/upgrade rear shocks





    madmax-im, Moabite, Mailman and 4 others like this.
  12. Machine

    Machine Race the wind Top Contributor

    Yikes bout those carbs . There are many around to find however .
    Bet ya a dollar that the counter shaft sprocket nut is loose
    YamadudeXS650C, Mailman and MaxPete like this.
  13. 5twins

    5twins XS650 Guru Top Contributor

    I've seen and cleaned carbs much worse off than that. That's not corrosion in there but rather the remnants of evaporated fuel, the "varnish" as it's called. Scrubbing with carb cleaner will remove it pretty easily. Don't throw the towel in on that carb set yet. Keep after that stripped pilot jet. Keep it soaking in penetrating oil and apply some heat to it when you try to loosen it. You may need to grind down some 1/4" screwdriver bits to make one that fits well. With a good fitting bit, a couple light taps using a hand held impact driver may break the jet loose.

    That plug doesn't look really black. Keep in mind that starting with the choke will blacken the plugs up pretty good and quite quickly. It takes a few miles of riding afterwards to burn them clean again.

    To do a proper cleaning, you'll need to remove the mix screws and their associated parts (spring, washer, o-ring) so you can blow cleaner through the passageway. If you flip the carbs over, you'll see a tower just in front of the slide area. The mix screw mounts in there .....


    The factory capped over the screw with a metal plug so you wouldn't fool with it's setting, and if your carbs haven't been messed with much, that plug may still be there .....


    It will have to be removed to gain access to the mix screw.
  14. xjwmx

    xjwmx It's just the unknown. Top Contributor

    I agree the carbs don't look as bad as you might think. To get the pilot jet out, if you can't get a bit to grab it, I'd take a Dremel with a cylindrical bit the width of a good screwdriver bit and make a slot. Use a long screwdriver bit with parallel sides at the tip instead of a screwdriver. Stuff paper into the hole in the jet so particles won't get through. Flush it out carefully after the grinding and before removing the jet. The mix screw caps, if carb cleaner will flow through all the pilot holes okay, you could leave it for last. In fact mine still have the cap and the factory adjustment and run fine.
    rbirkey and Mailman like this.
  15. 5twins

    5twins XS650 Guru Top Contributor

    I strongly suggest removing the mix screw prior to cleaning. If you spray carb cleaner through there, chances are good you'll turn it's little o-ring into melted muck.
    lakeview and YamadudeXS650C like this.
  16. rbirkey

    rbirkey TriumphBonneville.org

    Thanks to your hints and suggestions, I have been able to completely disassemble the carbs!

    Now I need to buy all the replacement parts possible:
    • needles
    • jets
    • valves/seals
    • gaskets
    Can I find everything I need on Niche Cycle? What range of jet sizes should I get?






    Mailman and MaxPete like this.
  17. 5twins

    5twins XS650 Guru Top Contributor

    Yes, you're going to want new mains and pilots, larger sizes than stock, but the needles and needle jets usually don't need replacing. That's a good thing because you can't get genuine ones anymore, only knock-offs. Be aware that these BS34 carbs use different types of mains and pilots than the BS38's you were working on. The mains are the large round style, Mikuni part #N100/604 .....


    ..... and the pilots are the BS30/96 type .....


    One size up on the pilots should be good (#45) but the mains will depend on your mods. One size up (to a #135) might do for only one mod like the pods, but more than that will most likely require more sizes up. If you plan the usual "pods and pipes" modding, I'd skip right over the 135 and get 137.5 and 140.

    You haven't quite disassembled everything. I see your pilot circuit air jets are still in the bell mouths. That's OK, they just flow air to the pilot circuit and rarely get dirty or plugged. You can blow through them to insure they're clear with them still in place. But, they are another tuning factor for your idle circuit. You can change them. Usually, you reduce their size by a couple. This lets less air in and makes the idle circuit richer. They don't have as big an effect as changing the pilot jet size so can be considered a "fine" tuning adjustment.

    I also see the metal plugs are still in place covering your mix screws. Personally, I feel they need to come out so you can access the mix screws. The tiny o-ring on the mix screw usually needs replacing by now, not to mention the screws are set very lean from the factory. The removal process involves drilling a 1/8" hole into the plug and threading a sheet metal screw into it. Then you grab the screw with vicegrips, twist and pull the plug out. The tricky part is not to drill too deep, not all the way through the plug. The mix screw is just below it and made of soft brass. Drill through and you often damage the screwdriver slot on top of the screw. To further ward off damage to the screw, it's a good idea to grind the sharp point off the sheet metal screw .....




    You'll notice a tiny hole in the center of the plug. Use this to judge your hole depth. The plug is about 3/16" to 1/4" thick. Drill a little bit and check the hole. Look at the size of that tiny hole in the center of the plug. Drill a little more and check it again. Keep doing this, drilling just a little at a time, until you see the tiny hole in the center of the plug begin to get larger. Stop drilling any further, you're almost through the plug.
    Mailman and rbirkey like this.
  18. xjwmx

    xjwmx It's just the unknown. Top Contributor

    All I can say for sure is if that happened to mine it wasn't a problem. But if he did remove the o-ring, he'd probably find it was flattened and hardened. I think the plug itself prevents significant air leaking.

    P.S. Is there a source for replacement needles now? Last I remember the best you could get new was a bad approximation.
    Last edited: Aug 6, 2019
    rbirkey likes this.
  19. 5twins

    5twins XS650 Guru Top Contributor

    You mean slide needles? I don't think originals are available, but if replacing it I think I'd go with one of the aftermarket adjustable ones they sell. And my choice wouldn't be the normal supposed "Canadian" needle, it would be this Cruzinimage kit. It contains not one but two adjustable needles, needle jets too, and doesn't cost much more than the MikesXS bare bones BS34 rebuild kits .....


    Granted, it doesn't contain the rubber plugs for covering the pilot jets but those can be found for $2 to $3 each. On the other hand, needles are about $10, needle jets about $15, so you get $5 less in parts but around $70 more.
    rbirkey likes this.
  20. fredintoon

    fredintoon Fred Hill, S'toon. Top Contributor

    Hi rbirkey,
    the cast wheels should be tubeless, check for a legend that says so stamped into one of the spoke webs.
    The seat pan could be re-upholstered with a flatter cover and foam to de-hump it.
    The front fender is also a fork brace. best you fit one or an aftermarket brace instead.
    Like most of the drum rear brake Specials, the bike has lost it's small trapezoid lower side covers.
    The stock '77 & newer front brake M/C's piston is sized to work the dual calipers the rest of the world got.
    Here's what I'd do to improve how the single front brake works:-
    Swap the stocker for an M/C with a ~1/2" diameter piston.
    Replace the time-expired fabric brake lines with s/st braid reinforced lines.
    Drill the bejasus out of the brake disk.
    (You get the same effect by adding a leftside caliper instead but that seriously increases the unsprung weight)
    MaxPete and rbirkey like this.

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