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Thread: Z50J - TB V288 & Yoshi TM-MJN 24 Carb issues

  1. #1
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    Z50J - TB V288 & Yoshi TM-MJN 24 Carb issues

    Hi,

    I have recently near completed my Z50J custom build.
    I have installed a TB v2 88 kit and also a Yoshimura TM-MJN 24 carb, although I seem to have no mid-top end power - top speed seems to be maxing out at about 45/50km.
    I have played around with the carb a bit and double checked most things although I am stumped (I don't have the greatest knowledge with tuning carbs).

    I have listed the mods below in case you see anything else that may cause the issues.

    Engine:
    - Z50J converted to 12v with taki rotor and crf50 12v crank
    - TB88 v2 top end
    - Taki heavy duty standard clutch
    - Exhasust - Over Racing up exhaust

    Sprockets
    - 13/37

    Carb
    - Yoshimura TM-MJN24
    - Pilot - marking 25 on it
    - Main - marking 56 on it
    - Needle - Marking MA on it, and set on middle clip

    Electrical:
    - 40th 12v harness
    - Standard crf50 cdi (I did have a TB CDI although it blew, unsure why)

    Any help greatly appreciated,

    Ben



    image.jpg

  2. #2
    Moderator dex's Avatar
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    One major problem is your gearing ,,,
    Need to go up to at least a 15 or 16 on the front , and drop to arround the 32ish on the rear ,, outright speed wiil dramatically improve .
    its engine oil madge ,,,
    Your soaking in it ,,!!

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    Thanks Dex, appreciate the feedback.

    I try some different gearing as suggested.

  4. #4
    Moderator dex's Avatar
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    Does it feel like the motor is crisp and developing smooth power all the way to its top speed ,,
    Ie ,, no flat spots , no bogging /running flat ..
    Revving right out to arround 9-10thou ,?
    its engine oil madge ,,,
    Your soaking in it ,,!!

  5. #5
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    Hey Dex, the first half throttle is smooth and responsive, but the second half/top end is a bit rough/sputtering slightly and subsequently slower than expected.

    I assume I need to look at some different jets, just unsure which way to go??

  6. #6
    Moderator dex's Avatar
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    If spluttering , " as long as float level is cool " ,,,needle position ,, play with the clip on the lower slots ,,, this allows more fuel in as the needle raises in the upper revs .
    ,jetting will be your next step . ,, main jet will be your target ,,
    Getting the smooth transition from the idle jet to the main is the main thing ,, and a singing top end .
    its engine oil madge ,,,
    Your soaking in it ,,!!

  7. #7
    Senior Member Alfie's Avatar
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    I found with 88 kit 15/35 was a good start point with that gearing it was up around 80km/h
    As far as the carb mine was good out of the box you only need to play with the needle

  8. #8
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    Thanks guys.
    I have ordered some new sprockets, will start from there and see how we go with the carb after that.

  9. #9
    Senior Member Alfie's Avatar
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    Benny D how did you go any luck?

  10. #10
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    Hey mate, I have been slow progress on the bike lately.
    I fitted some new gearing last w/e, although still the same result, it seems like it is mostly carb/jetting related. Me being me, I have been misreading the main jet size which I originally though was a 56, although I had it upside down and it is actually a 95. The bike seems to bog down at around half throttle, so I have got my hands on some smaller main jets which I plan on giving a go this w/e. I will keep you posted how it goes.

  11. #11
    Moderator Diggs's Avatar
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    My input is "jetting"

    My other feedback is, that's a bloody nice bike mate!
    Rigby "No dude, you're doing it wrong! Righty-tidey, lefty-losey! Not lefty-tidey mess it up because you're a loser!"

    ZRX1200S, RGV250 VJ22, Skyteam T-Rex, Z50A K2U '72, Z50J1 '78, Z50R '82, Tonelli Gorilla

  12. #12
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    Quote Originally Posted by Diggs View Post
    My input is "jetting"

    My other feedback is, that's a bloody nice bike mate!
    Haha thanks Diggs! I need all the input I can get.

    I see you are from Brisbane, I am in Melbourne at the moment although moving up to Brisbane in a month or so with work. I notice there is quite a community of Brisbane mini riders, hopefully will get in touch when I am up there and get involved with the mini scene!

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