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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.

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    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 ,,!!

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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?

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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, Z50J1 '78, XV250 Virago

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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!

  13. #13
    Senior Member Alfie's Avatar
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    Benny D ive just played around with the mjn-24 I bought for my takegawa 106, the carb ran straight out of the box with the stock jets and settings( 25pilot & 95main) however its running rich. I ended up working my way down on the pilot jets from 25,22.5,20,17.5 to find the 15 pilot is good to go, idle was nice and cold starts actually started with the choke on and easy once warm it starts 1st kick no throttle. I am going to start on the main jet next as I think its still running a bit rich top end, I havnt needed to touch the needle yet as the transition from pilot to main is still smooth and not missing. I'm thinking mine should be around the 90main jet mark, on that I would try around the 89main for you 88c.

  14. #14
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    Thanks Alfie.

    I have recently moved from Melb to Brisbane so havnt touched my bikes in a couple months.
    Hoping to get stuck back into them soon. Appreciate your assistance/feedback mate.

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