Yamaha XS650 twin

Discussion in 'Motorbike Technical Discussion' started by Dave, Jun 26, 2007.

  1. Dave

    Dave Guest

    After a recent bout of twin-bashing on rec.motorcycles, I dragged out my old
    XS650 parallel twin last night and took it for a ride. The ride was good, I
    enjoyed the sound from those skinny chrome mufflers even if the 650 corners
    like a pig compared to the sportbike I usually ride. Could do without the
    enormous vibration too, particularly in the footpegs.

    When I fired it up, naturally it backfired a bit not having been run since
    last year. I had drained the carbs, blah blah blah so no worries. The
    backfiring seemed (and that's all it was, seemed) to be coming from the
    right pipe only. I put my hands behind the two pipes, and there was WAY WAY
    more pressure coming out of the left pipe vs. the right. Intuitively this
    seems very wrong. First suspecting rusty headers (couldn't remember just
    how loud it was supposed to be) where they sweep up into the mufflers I
    checked them carefully... no holes. Both pipes got hot at about the same
    rate near as I could tell without an infrared thermometer. The temp of the
    exhaust coming out of the pipes "seemed" about the same.

    Anybody have any thoughts? Bad spark plug?

    BTW the bike ran great, enough power to remind me that I never did get
    around to replacing the front sprocket this winter... the engine sounds fine
    and seems to run fine once warmed up marginally.

    Dave S
    Dave, Jun 26, 2007
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  2. Dave

    Dave Guest

    1980. Sorry.
    I'll have a look at the points and check the gap after I stick a new plug
    in. Never have replaced the plugs on that bike.
    Dave, Jun 26, 2007
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  3. Dave

    Dave Guest

    I mean I WOULD have looked at the points if the bike didn't have electronic
    ignition. Oops.
    Dave, Jun 26, 2007
  4. I'd expect this, if the right hand pot wasn't running right.
    Just an engine waking after a long sleep.....
    So leave it alone. If it ain't broke, don't fiddle with it.

    Lovely bikes, btw. I've owned four or five and want another.
    The Older Gentleman, Jun 27, 2007
  5. <snip>

    Your comment about the sprocket reminded me - US models run lower
    gearing than European. Going up one tooth on the gearbox sprocket
    makes them run much more relaxed at cruising speeds. Of course, you
    lose the acceleration, but these days nobody uses an XS650 for drag
    starts, do they?

    The taller gearing improves the fuel consumption markedly, as well.

    And if you want a neat tip, drill a hole in the sprocket cover,
    immediately above the sprocket, and route the rocker box breather pipe
    down to it. Obviously, make sure the hole is the right size for the
    pipe to be a tight push fit in it. The oil fumes from the top end come
    down and lube the chain.

    God, I'm getting the yen for another XS650 now. <Scans Ebay>
    chateau.murray, Jun 27, 2007
  6. Dave

    Hank Guest

    Less volume out might mean less volume in, from a sticking carb slide maybe?
    Or reduced pumping efficiency caused by leaking valves or stuck rings?
    Hank, Jun 27, 2007
  7. I bet there's still nothing wrong with it, now it's been used....
    chateau.murray, Jun 28, 2007
  8. Dave

    Badger Guest

    Do these bikes have a balance pipe or collector box?, it may be that the
    silencer has corroded internally and it is partially choked. If it is one
    header to one silencer with no link pipes, then the above does not apply.

    Are the carbs in sync?, if you have a carbtune ( or similar ), these are
    great for troubleshooting.

    Can you access the slides through the airbox?, if you can, lift both slides
    and then let go. They should drop together, and they should be damped. If
    one slide seems to stick, you probably just have a small amount of
    corrosion on the slide, easily sorted.

    That you said it runs great doesn't point to any major mechanical grief.

    Lovely bikes. I quite fancy a cafe racered one.
    Badger, Jun 28, 2007
  9. Dave

    Dave Guest

    Hmmm... that really doesn't look that difficult to do... the only thing that
    would likely confuse me is moving the correct hall-effect sensor magnet in
    the correct direction. I've never really done any serious engine mods like
    that but boy, it would sure make this bike a lot more rideable for me if it
    had less vibration. It looks like the only machining that needs be done for
    the whole procedure is the notch cut out of the crank cheek.

    Has anyone replaced the rubber handlebar vibration dampers (p/n 13119-001)
    with something stiffer to get the mush out of the steering? You'd have to
    for any kind of handling gains... if I can tame the vibes maybe I'll think
    street tracker.

    Dave S
    Dave, Jun 28, 2007
  10. No.
    The Older Gentleman, Jun 28, 2007
  11. And the camshaft?
    The Older Gentleman, Jun 28, 2007
  12. Dave

    Mark Olson Guest

    Hacksaw, JB Weld.
    Mark Olson, Jun 28, 2007
  13. I was waiting for someone to say 'angle grinder'.

    Wrong ng.
    The Older Gentleman, Jun 28, 2007
  14. Dave

    Dave Guest

    Mmmmm, good point. Guess it might run a bit rough what with the valves
    operating 83-degrees out of phase with the piston...
    Dave, Jun 28, 2007
  15. Dave

    Dave Guest

    Thanks. I'm very intrigued, will contact them for pricing. Do they build a
    new cam, or would I send mine to them for modification? Likely the latter
    unless I want to spend $500.
    Dave, Jun 29, 2007
  16. You'd have to sort out the ignition, too.....
    The Older Gentleman, Jun 29, 2007
  17. Dave

    Dave Guest

    Dave, Jun 29, 2007
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