Viewing 7 posts - 1 through 7 (of 7 total)
  • Author
  • #6041
    old red eyes

    My recently acquired KZ b3 starts easily and runs nicely up to 4000 rpm and cruises smoothly at that engine speed. My problem starts when I try to accelerate from there, sometimes it pulls quite well but most of the time it stutters and struggles to increase revs , it’s also prone to popping a bit on the overrun, I am suspecting dirty carbs as the bike has only done about 40 miles a year for the last 8 years.
    I now have them off the bike and partially stripped down, I’ve got to say I am used to working on small capacity Hondas and have never worked on anything quite so complicated.
    Where best to start ? And any tips and shared knowledge greatly appreciated.


    Good luck HaHa.
    They are not much more complicated than the little Hondas, it’s just more of them!
    The same principles apply, start with an exterior clean then with a clean tidy worktop strip placing parts in order as you remove them.
    The only extra bits are the diaphragms connected to the top of the throttle shuttle, these neeed to be checked for small holes or splits.
    Clean, inspect and reassemble.
    Pay particular attention to the gasket which is very important to the smooth running.
    You problem if it is carburation sounds like it is either, fuel flow into the carb, float hight, blocked holes on the emulsifier, blocked main jet, float hight or a split diaphragm.
    Popping on the overrun may be a leaking exhaust or inlet rubber, if no problem found adjust the pilot screw in on the offending side.
    Please note it is very difficult to explain things without actually being there but I tried 😉
    If all that fails try some carbs off another bike as the standard ones seem very temperamental, But to be fair mine work fine 😉

    old red eyes

    Thanks Mike will get in about them after work tomorrow.


    That’s great advice Mikeonabike.

    |My initial thoughts are that your main jet is playing up. There could be several reasons for that as explained by Mikeonabike.

    When you have access to the carbs before you strip them down lift the sliders together and make sure they drop smoothly and together. If one is faster than the other this could indicate a diaphragm problem.

    If the carbs turn out to be fine then it could be the strength of the spark.

    One of our members (Trevorbuster) had a similar issue. He had a low voltage reading at the coil so a weak spark was present. he fitted a relay to give a coil feed direct from the battery which he claims has massively improved his running. He is not an internet kinda guy (as is the case with several members) but has sent me ths details which I will post up in the near future,

    old red eyes

    Initial findings, one of sliders wasn’t sliding free gave it a light coating of very thin oil and feels a lot better. Inside of tank is very rusty causing a built up of crud at fuel taps, right hand feed was almost blocked. Tank on bench full of caustic soda for next few days.


    Another area to consider is the ignition advance/retard unit. This only comes into use as the revs increase and if it gets sticky through rust n crud can drag it’s heals in operation.


    Hi Andy,
    that was my first thougt as well when reading this post.
    Especially when it pops into the exhaust. A fixed timing advancer can cause these issues. Needs disassambly, some cleaning and greasing (only inside!) to work again.
    It is always a good idea to check the timing advancer !

    Prior to disassambly and just to check, remove the ignition cover, keep fingers, children and pets away and start the engine. From approx 3.000 rpm you should see the weights of the centrifugal governour moving to the outside / a larger radius. If they don’t do that, you have found the culprit.

    Not sure with points ignition of the Bs, but the same mechanical timing advancer is used with the pointless ignition of the LTD. I use WD40 or similar to lubricate that stuff.
    Will that work with the Bs as well, if used carefully ?

    Cheers, Michael

Viewing 7 posts - 1 through 7 (of 7 total)
  • You must be logged in to reply to this topic.

Share this