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XS750 carbs on a 650? (obviously only 2 of the 3...)

Discussion in 'The Garage' started by joestella28, Aug 19, 2016.

  1. joestella28

    joestella28 XS650 Member

    Hi All,

    I'm about to start a build and have everything to get the engine running... except for the carbs...

    the XS650 was taken apart 10 years ago and as usual, some things have gone walkies, the carbs being one of them. Now as with most of us, I have grand ideas and don't intend keeping the engine standard for long and had always intended upgrading from standard carbs. As such, I have a set of (three) XS750 carbs kicking about, with some re-jetting would two of the three be suitable to get the bike running in standard form?

    Many Thanks,

  2. weaselbeak

    weaselbeak XS650 Junkie

    They both ran BS38 carbs, so why not?
  3. fredintoon

    fredintoon Fred Hill, S'toon. Top Contributor

    Hi Joe and welcome,
    like weaselbeak sez, why not?
    You could also solder up some copper plumbing fittings into a manifold to run just one of them.
    Or go t'other way with the manifold and run all three.
  4. grizld1

    grizld1 Grumpy old man Top Contributor

    OK, here's (maybe) why not. Center-to-center spacing of XS650 carburetors is 120 mm., which does not translate to any spacing you can get out of an XS750 bracket, choke rod, and throttle shaft. So you'll need to either fabricate a custom bracket (easy), choke rod (moderately easy), and throttle shaft (very hard), or scavenge those parts from a pair of 1976-79 BS38s for the XS650.
  5. 5twins

    5twins XS650 Guru Top Contributor

    I'm pretty sure the 750 carbs are BS34s, not that it matters much for 650 use. As Griz said, the main stumbling block will be correcting the spacing between the carbs.

    If you did get some 650 carbs, the 750 set could be a good source for some extra parts. The alloy tops are a nice upgrade for the 650 BS34 "tin tops". The #135 butterfly plates also match the 650 BS34s.
  6. weaselbeak

    weaselbeak XS650 Junkie

    By son has an XS750 he bought as a donor bike for tractor pulling stuff. It has BS38's.
  7. angus67

    angus67 Welder's penetrate deeper!!

    If you put those alloy tops on 34, be mindfully that they are a lot thicker than the tin tops. I put a pair on my 34s, and started it. The thicker tops made the throttle open 1/8.....throttle cables need to be adjusted looser, almost as loose as they would go.
  8. joestella28

    joestella28 XS650 Member

    Cheers guys, I've got nothing to loose so might as well give it a go :)
  9. Another 10 year project. :D
  10. Hi Joe, I fitted GPZ500 carbs to my tracker, very easy mod, much lighter than the originals and I found them very easy to set up, also can be cheap on Ebay. I'm near Swindon - where are you in the UK?
  11. joestella28

    joestella28 XS650 Member

    Hi All, I've been surprised with how straightforward it is to space them out to be honest. Like I said, I'm only going to use them to get the engine running on a stand before the real mods start. After that point I'll get either some more modern CV carbs of some VM's.

    I'm based in Norfolk and am a long way off being able to ride the old XS :D

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