• Hello,

    does anyone know where to buy a new Throttle-Spring?
    I mean the big one that is at the end of throttle cable and goes into the carb.

    alt text


  • At Mikuni and Yamaha dealers it is out of stock and no longer available😧

    Found a supplier, that has the specs, nearly equal the original spring I hope

    While Im at it, what would you suggest to get for carburetor adjusting
    for a "stock" 4BL that has no more known restricted parts?
    main jets in 230,240,250? others?
    which idle jets?


  • @chris
    I’d look for a kit online. Full range. Why do you want to change the jetting?...


  • Hi, I want to change the jets because I dont know whats in there at the moment
    The whole bike was not used for 6 years, it startet after the third kick, but it was idleing at 5000 rpm and I couldnt get it down
    and it was dying with too much gas-pull, also the gas was hanging a bit in the end position

    What is the full range you mean?


  • Sounds like an airleak to me.


  • @Calum

    That might be possible.
    I didnt check the airfilter before starting the long time sleeper 🤦
    After opening the airbox I found the filter was crumbling apart
    I could image that this was causing it, but wouldnt that mean less air instead?
    Even after opening the carb and realising its not even slightly dirt in there Iam wondering what caused the high idle rpm

    maybe carb itself leaking?
    I have ultrasonic cleaned all the parts, will redo all screws, hoses and gaskets and check again

    Whats the correct main and idle jet, is 240 and 25 okay?


  • wow! I wouldn’t mess with the jetting until you’ve found the cause of the high revving. A split in the inlet manifold would be first try...
    How long have you had the bike? How long has it been high revving? Have YOU altered anything?
    P.S. Full range just means all the different sizes. I’ve seen them being sold as a set...
    P.P.S. What is your native language?...


  • @SpookDog
    going to stock jets is no messing around I think
    the inlet looks okay
    I bought it years ago, rode it for 2 month without anything unusual and put it to a six year sleep, till now.

    The idea of this start was to burn in the new exhaust paint, check if the cooling system that I partly redid was proof and get the motor warm for an oil change after

    I let it run for ca 20 min till the cooling system was leaking on a hose

    This run was with the 6+ years old crumbling airfilter, what I realised only later

    im from ger


  • @chris
    Guden Tag then bud! 😎

    Going back to standard would be bestest, but if it was running good 6 years ago I’d leave it until you work out the problem with ticking over @ 5000rpm! Even having no filter wouldn’t cause it.
    Have you removed all the filter bits and cleaned out the carb since finding it, are you sure the slide is closing fully? No cable catching on an adjuster?
    I usually spray a bit of carb/brake cleaner around suspected areas while the bike ticks over. If there’s a leak it usually settles down to normal revs...
    It really does sound like a big air leak between the casing and the carb...


  • @SpookDog
    Danke sehr

    After that I cleaned the airbox and put a new and oiled filter in there.
    Then I opened the carb, 5 screws were done and had to be drilled out, was a 2 hour pain in the ass work, I will use better screws with hexagon drive soon
    I wondered how clean the carb was inside
    The housing parts etc. are now ultrasonic cleaned and the spare parts available are ordered

    Do the gaskets for the housing parts have to be oiled during assembly?

    What would be the correct torque for the housing screws?


  • @SpookDog

    Now in hindsight I remember the choke's nut was loose
    I didn't pay any attention to that, maybe that could be the cause of the air leak you mentioned.

    **Do the gaskets for the housing parts have to be oiled/greased during assembly?

    What would be the correct torque for the housing screws?**


  • @chris
    I’d use a small amount of grease myself. The bolts I do by instinct. You’d need a mikuni manual or search their site. It’d be almost unmeasurable unless you have a very delicate torque wrench...


  • @SpookDog
    Yes, precisely because it is difficult to estimate, I always use a torque wrench on my rides to tighten if possible and the values ​​from the manufacturer are available
    Mikuni manuals do not have this info apparently

    I guess 5nm would be max for the m4 screws, and about 3nm for the brass stuff, but official data would be nicer


  • @chris
    As long as the threads are all clean, I do them all finger tight, then 1/4 to 1/2 turn. As long as they are all the same. That’s what’s important...


  • Yeah torque wrenches have their uses, but with soft metals you have to be really careful, much better to do it by feel. It's not something that undergoes massss of stress so torquing it isn't absolutely necessary.


  • I found new informations, here are the essential tightening torques:
    Float chamber screws: 2.0 Nm
    Main jet: 2.0 Nm
    Slide cover screws: 2.0Nm
    Screw slide lever: 3.5Nm
    Drain screw: 2.0Nm

    carb housing gasket at https://www.gasketguru.co.uk/

    Also i found the throttle-spring at http://www.motocarb.com/tm-parts.html

    still looking for the nozzle assembly

    @Calum

    can you allow to edit posts, then I could reformat opening post and edit this infos? could be nice for others also looking for parts and stuff


  • @chris Create a new thread with the appropriate title and formatting, and I will sticky the post for you bud!


  • @Calum
    okay, will do that later when the carb is complete