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  1. #1

    Join Date
    May 2017
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    Moded yx 140 PE 28 keihin

    Hello guys, im new to the forum. I was searching on internet for carb tuning and i found this site, and is very informative. Can you help me with jetting on my pitbike.

    Motor is yx 140 gen3, motor has Hi-speed piston 56mm, z40 cam set, light port and polish not removed valve guides, 0.5 base gasket and 0.5mm cooper basket, daytona style ORK. Iam using 1/4 throttle and when i flick throttle hard it dies on me and i have from idle to 1/4 throttle stumble.

    Jetting specs: 40 pilot 1turn out JJH needle 95 main.
    Valve specs: 4in and 6 ex thou.
    plug: cr7hix and its showing chokolate brown on electrode and tip.

    Is my jetting off or its to small of a bore to handle 28mm ??

  2. #2

    Join Date
    Dec 2014
    Location
    west coast NZ
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    Quote Originally Posted by stindeee View Post
    Hello guys, im new to the forum. I was searching on internet for carb tuning and i found this site, and is very informative. Can you help me with jetting on my pitbike.

    Motor is yx 140 gen3, motor has Hi-speed piston 56mm, z40 cam set, light port and polish not removed valve guides, 0.5 base gasket and 0.5mm cooper basket, daytona style ORK. Iam using 1/4 throttle and when i flick throttle hard it dies on me and i have from idle to 1/4 throttle stumble.

    Jetting specs: 40 pilot 1turn out JJH needle 95 main.
    Valve specs: 4in and 6 ex thou.
    plug: cr7hix and its showing chokolate brown on electrode and tip.

    Is my jetting off or its to small of a bore to handle 28mm ??
    Hey bud this site is awesome!!, welcome, I have never had a 140 with a pe28 but do have 3x z160ho's with various mods on different engine's, I dont have anything bigger than a 26mm oko on any of the 3 but ii'm sure my 160ho with v2 head would benefit with a pe28.

    I am definitely not an expert on carb tuning but even my stock 160 is running a 39 pilot so just guessing that your pilot jet is too big?.......

    valves should be set at .003inches/.08mm inlet and .004inches/.10mm exhaust.

    hope this helps.

  3. #3

    Join Date
    Apr 2013
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    have a look at you spark plug, it will most likely be black.
    try turning airscrew out to 2 turns and see if it gets better,if so then get a
    smaller PJ and lower the needle too...

  4. #4

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    May 2017
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    Hi guys. I set valve clerences, and plug clerance. I have droped to 38PJ, 92MJ and JJH on 3 spot. Its almost perfect and low throotle power is so good instant whelie. Thank you very much for help.

    Plug picture:
    20170530_111905[1].jpg

  5. #5

    Join Date
    Dec 2014
    Location
    west coast NZ
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    Quote Originally Posted by stindeee View Post
    Hi guys. I set valve clerences, and plug clerance. I have droped to 38PJ, 92MJ and JJH on 3 spot. Its almost perfect and low throotle power is so good instant whelie. Thank you very much for help.

    Plug picture:
    no worries mate, been through it all myself and know how frustrating it is!
    such a relief to get it right/close...

  6. #6

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    that spark plug looks terrible! :-/ try a fresh one and maybe it'll even be better...

  7. #7

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    This is jetting with new plug. 20170603_173651.jpg

  8. #8

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    what do you do to get throse threads so greasy??
    i think it needs some more riding to be able to examine the spark plug.
    are you getting better resuts from changing the jets and needle too?

  9. #9

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    i dont know the engine is in good condition has a new piston and good compression. Iam using 100 octane gas. I have now 95MJ. And i retarded a little ignition. The power is good from 1/4 to WOT. I know you loose some bottom end with big carby.

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