Changed main jet
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Thread: Changed main jet

  1. #1
    Senior Member jannaruto's Avatar
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    May 2017

    Changed main jet

    Hey guys,

    So me and my dad purchased some used parts for the TW, a shitload of stuffs and a 125 engine for very few bucks, we plan to renew everything to proper work
    In this box there was a carburetor, a TK one, but different model from mine one, still I opened it and found inside a main jet 118
    Mine one is a 116
    I cleaned it and decided to change
    Difference man!!!
    Mid-High I feel more power, even in 5th gear you can feel a bit of pulling under your butt, even a bit on hill

    I ordered in December some more TK jets, still waiting for arrival, but very surprised how just +2 in size made a sensible difference (driving the bike every day everything appears very clear and recognizable to me)

    If you guys have a chance of changing jets I recommend it, even just +2 in size will definetely improve your overall mid-high range

    Also I am still using my custom exhaust (modified KTM Supermoto one) so top speed is only about 115-120 (yes I recovered something in speed) but don't want to change again to the stock one to see that 130, acceleration is quite more fun to be honest :P

    I wanted to change the pilot jet too, but without removing and turning the carburetor sideways the screw bits I have are a bit too short for this purpose, also the TK carburetor I opened has a 39 inside, I doubt is bigger than mine which is a TW200 and should be already 40 or 42 by itself, I will probably change and verify that when the Whole new set from Aliexpress will be here and also I will relace the Airbox to carburetor boot with the TW125 one being something like 2cm longer so I will get a more consistent "perfect seal"

  2. #2
    Senior Member SportsterDoc's Avatar
    Join Date
    Jan 2017
    Southern Nevada
    The best jetting is dependent upon operating altitude.
    Plug color will help.
    Also, if you are able to discern between balking/hesitation from leanness or blubbering from richness, that is a big indicator.

    For the main jet, running wide open throttle, if slightly backed off and it gains speed (slightly closing throttle reduces incoming air, while the main is still sucking about the same), then it is too lean.

    For the pilot, if 2 3/4 to maybe 3 turns out on the mixture does not optimize idle, then a larger pilot is needed...or there is a vacuum leak.
    jbfla likes this.
    2014 Honda CB1100
    2018 Yamaha XT250
    2016 Moto Guzzi V7 II
    2017 Yamaha TW200
    2012 Triumph Bonneville
    2002 H-D Sportster 1200 Sport
    2003 H-D Sportster 883
    1976 Honda CB750F
    1975 Honda CB360
    1970 Yamaha CT1
    1972 Yamaha CT2
    1972 Yamaha AT2/CT2
    1970 Honda SL350
    1970 Honda CL350
    1967 Honda CL160
    1967 Honda CB160
    1962 Honda CA110

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