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Do carbs Jingle under lean conditions?

Discussion in 'The Garage' started by xonix_digital, Sep 27, 2018.

  1. xonix_digital

    xonix_digital XS650 Addict

    Hi all,

    I have a 1980 xs650 with the carbs from a 1976 (Mikuni BS38). I have it starting and idling fine, and to be honest it feels like it's running fine up and down the road, but I am hearing a jingle sound at certain points when I am early on throttle or off throttle while moving.

    Do these things jingle if they're running lean? Could it be pinging? What's the best way to tell for these old ladies? I've never ridden another Xs650 so I can't be sure how it's supposed to feel.

  2. xonix_digital

    xonix_digital XS650 Addict

    Posted before searching. My bad. Found what I was looking for. Mods can delete.
  3. angus67

    angus67 Welder's penetrate deeper!!

    Mods wont delete a thread like this because subsequent replies could be used for learning purposes for new learners. I assume you adjusted your cam chain?
    gggGary, TwoManyXS1Bs and peanut like this.
  4. fredintoon

    fredintoon Fred Hill, S'toon. Top Contributor

    About the noises:-
    " letter from a new owner:-
    Dear Mr. Bugatti, I just bought one of your cars and it's engine sounds like a bucket of bolts being poured onto an iron plate.
    Reply from Ettoire Bugatti:- From what you describe, your engine is running perfectly."
    And it's the same with an XS650. It's an unbalanced air cooled twin full of ball and roller bearings and no, it ain't quiet.
    You just gotta learn the difference between it's normal clatter and the noise of an imminent engine failure and that will
    only come with experience and advice so yes, keep asking.
    gggGary and robinc like this.
  5. peanut

    peanut XS650 enthusiast & inveterate tinkerer Top Contributor

    if you post the solution you found , other members might benefit ?
    This is a community where we share our knowledge and experience for the benefit of everyone.

    it sounds like your engine is pinging due to detonation.....google it before you hole your pistons.
    Also check your plugs for evidence of an excessively lean mixture
    gggGary, Wulfbyte and TwoManyXS1Bs like this.
  6. xonix_digital

    xonix_digital XS650 Addict

    Hey all,

    Thanks for the comments. I have confirmed that the cam chain is properly adjusted, cleaned both carbs, and reset the floats and idle. One side still runs hot and pings under load. I have confirmed that it is pinging/detonating.

    Both plugs are a nice medium brown so at least it's not that bad yet.

    I believe that I have some failing O-rings on the left side carb and will rebuild with a new kit and increase both main and idle jet sizes if the problem persists.

    Ant other suggestions? Something I'm missing?

    gggGary likes this.
  7. Jim

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

    Check that your ignition timing isn't too far advanced.
    grizld1, gggGary, peanut and 2 others like this.
  8. xonix_digital

    xonix_digital XS650 Addict

    I'll check that in the morning. I have a new pamco ignition that I haven't installed yet. Ill see what's up with the timing and report back.
    gggGary likes this.
  9. 5twins

    5twins XS650 Guru Top Contributor

    Many of us are in favor of running the timing a couple of degrees retarded. It will help insure against pinging (why I initially did it) and I think the bike actually runs better, performs better at higher speeds and RPMs (why I'll continue to do it).
    TwoManyXS1Bs and robinc like this.
  10. xonix_digital

    xonix_digital XS650 Addict

    Is there a write-up somewhere on how to set timing with the stock 1980 electronic ignition? I am having a hard time finding one.
  11. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Timing is fixed on the TCI ignitions. The pickup can be moved but caution should be used when doing this, it is set from the factory.............

    If the carbs have a known air leak this should be fixed before doing or changing anything.
  12. xonix_digital

    xonix_digital XS650 Addict

    Hi all,

    After striking out on adjusting my timing with stock electronic ignition, I moved back to mechanical faults.

    I found that there were bad o rings at the fuel mixture screws mucking up my sync. I replaced both o rings and resynched the carbs but both mixture screws need to be 4-5 turns out before she idles right.

    Now, she stumbles equally when first initiating throttle, and jingling (detonating) on normal and heavy throttle.

    All of this leads me to believe that the bike is lean under all conditions and needs larger pilot Jets and main Jets.

    Anyone agree or disagree?
    I am running 135 mains and 27.5 pilot Jets with air cone filters (yes the crappy ones). Any way to tell how many sizes up I need to go from the idle screw settings?

    For time sake, I have ordered 140 and 142.5 mains, and 32.5 and 35 pilots from Mikes XS.

  13. 5twins

    5twins XS650 Guru Top Contributor

    You should positively I.D. the year of your carb set before you try re-jetting them. Re-jetting is based on what was stock in the particular year carb set you're using. In your 1st post you claim the carbs are from a '76, but the '76-77 carb set doesn't have o-rings on the mix screws. However, the '78-'79 carb set does so maybe that's what you've got. Also the 135 main and 27.5 pilot were not stock sizes for the '76-'77 carb set, but they were for the '78-'79 set. But it's possible to find those sizes in a '76-'77 set because that's what comes in many of the aftermarket rebuild kits. I know, it's wrong, but they've been making and selling those kits for years like that.

    To positively I.D. your carb set, take a look at the intake bells where the air filters clamp on. The '78-'79 set will have 4 round holes along the sides, the '76-'77 set will only have 2 .....

    robinc likes this.
  14. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Your already 5 times over the main recommend size and 6 times over the recommend pilot jet size and 3 1/2 to 4 times out on the pilot screw recommendations.........

    2 things..........

    1 Post pics of the carbs so we can verify they are the 76/77 Carbs........There is no way the 76/77 carbs with this set up is correct.......

    2 Get rid of the pod filter, (you know it is a problem), and get a uni filter or go back to factory air-boxes.........This has to be done before the jetting can be fixed
    robinc likes this.
  15. xonix_digital

    xonix_digital XS650 Addict

    Attached Files:

  16. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Makes a difference.....The jet sizes are now correct for 78/79 Carbs............Jumping 2 sizes!!........Recommended the jets should be bought as Makuni Genuine. No guarantees aftermarket jets are not Chinese sized........Pay for what you get...........

    Bookmark these links........Throttle shaft seals......Tips.

    Update on throttle shaft seal replacement suppliers post #13

    xonix_digital likes this.
  17. 5twins

    5twins XS650 Guru Top Contributor

    No, don't get those stubby UNI's with the capped ends, get these longer, all foam ones, UNI part #UP4200 for your BS38s .....


    As far as oiling them goes, the black foam they're made from is finer than the green foam used on many other UNI filters. The special foam filter oil they sell is too thick and tacky for them and will clog them. Just use a 50-50 mix of gas and motor oil.
    robinc likes this.

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