To shim or not to shim needle
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  1. #1
    Senior Member kennethshaw's Avatar
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    Hey guys,



    I've taken my carb off of my 2006 TW and want to shim the needle. I am pretty sure I need them since any time I roll on the throttle quickly, the bike stalls. Can you guys advise on how much to shim height wise? I'm also upping the jets from 126 to 130.



    Thanks.



    Ken

  2. #2
    Banned qwerty's Avatar
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    Quote Originally Posted by kshaw View Post
    Hey guys,



    I've taken my carb off of my 2006 TW and want to shim the needle. I am pretty sure I need them since any time I roll on the throttle quickly, the bike stalls. Can you guys advise on how much to shim height wise? I'm also upping the jets from 126 to 130.



    Thanks.



    Ken


    Something funky about your jet sizes. 125 is the 49-state jet, 128 is the California jet. The rest of the world gets the 132 jet. There is also a 130 jet, but not used on any TW. The 126 jet is a new one on me.



    Make one change at a time with your carb. First do the main. Test. Then redo the main if it isn't right. Test. Repeat until the main is right. When the main is right, start messing with the needle. Test. Mess with the needle. Test. Repeat until the needle is right. Then start with the pilot screw.



    Reason being is the main affects the midrange much more than the needle affects WOT. If you set the needle, then mess with the main, you'll likely mess up the needle. If you set the main, then mess with the needle, you are not very likely to mess up the main. Same relationship between the needle and pilot screw--the needle has much more effect on idle than the pilot screw has on midrange.



    Increase main jet size one step at a time. Power will improve with each step. When you reach the jet that causes a loss of power, back up to the next smaller. Check to see whether it or the next smaller yet provides the most power. If two jets perform the same, stick with the smaller jet if the whether is hotter than usual, or the bigger jet if the weather is cooler than usual.



    Repeat with the needle--adjust by steps and test at each step. When there is a loss of performance, back off. If using washers, sometimes they are two thick. Washers can be thinned by dragging them across emery paper. Usually, such small washers are stamped, and on side has a little flange around the edge of one flat, which is easy to knock off. you can also thin washers on the anvil part of a vice with a hammer held carefully so the hammer face strikes parallel to the anvil.



    Repeat with the pilot screw--gradually adjust until there is a loss of performance, then back off a bit.



    I suggest that you replace the bowl and suction piston assembly cover screws with stainless allen heads so the low quality OEM screws don't strip/wear to the point of useless.




  3. #3
    Senior Member craig0ry's Avatar
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    I would like to resurrect this ancient thread to pose a question.

    If I've adjusted the main (116 is about perfect for my conditions) and I've got my pilot and idle set up just right, will I still see an "improvement" by shimming the needle? I don't notice any surging or "problems", but it would always be nice to see a little more midrange "snap" from the throttle.

    In any case, it's not a difficult mod so I'm going to try it (perhaps this weekend), but I wasn't sure if this a "performance" enhancement mod or a "correctional" mod.

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  5. #4
    Senior Member RockyTFS's Avatar
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    Quote Originally Posted by craig0ry View Post
    ...., will I still see an "improvement" by shimming the needle? I don't notice any surging or "problems", but it would always be nice to see a little more midrange "snap" from the throttle...
    I would call it a "correctional" mod. However, since the needle has most of it's influence in the mid range, and two shims would enrichen that range, you might notice a little better acceleration....I think the effect would be minimal, since these carbs don't have an acceleration pump. It's so easy to experiment though, so why not?

    WHEN YOU ARE RE-INSERTING THE NEEDLE ASSEMBLY, DO NOT FORCE IT EVEN THE SLIGHTEST BIT!!!!!!! IT SHOULD JUST DROP IN WHEN YOU ROTATE THE CARB BODY!!!!

    Don't ask me how I know this.....
    Rocky
    2018 TW200
    2014 BMW R1200GS LC

  6. #5
    Senior Member rurlndum's Avatar
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    Something funky about your jet sizes. 125 is the 49-state jet, 128 is the California jet. The rest of the world gets the 132 jet. There is also a 130 jet, but not used on any TW. The 126 jet is a new one on me.



    My 2006 also had a 126 jet. Went to a 128. Can't find a place to buy a 130.

  7. #6
    Senior Member trailscout's Avatar
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    Quote Originally Posted by kennethshaw View Post
    Hey guys,



    I've taken my carb off of my 2006 TW and want to shim the needle. I am pretty sure I need them since any time I roll on the throttle quickly, the bike stalls. Can you guys advise on how much to shim height wise? I'm also upping the jets from 126 to 130.



    Thanks.



    Ken
    The carb can't see the needle when you roll it on. Have to get close to 1/2 throttle before the needle will have a noticeable effect. I'd look to your slow/pilot jet. I went to a #45 and it solved my "roll on" problem.

    The cut away in the slide has an effect in the same area but a larger slow jet should do the trick.

  8. #7
    Junior Member Paladin's Avatar
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    My 2008 TW has a 126 main jet as well from the factory. If you are looking to shim the needle I found that the small washers used on the Idle mixture screws of Mikuni carbs are a perfect fit and they average .020 in thickness. Most good dirt oriented bike shops will have these. If the parts professional doesn't know what you are talking about, tell him it is the little washer that goes between the spring and o-ring on the idle mixture screws. The exploded view of the parts diagram of the carb usually shows this. It is important that the washers you use are not larger in diameter than the white plastic keeper on the needle or they will not fit properly in the spring seat...And don't forget that little spring between the b

  9. #8
    Senior Member rurlndum's Avatar
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    My 2006 is running fine at a 5,000' elevation with a #130 main jet.

    Yamaha part number 288-14343-65. Got my jet at BikeBandit .com.

    Stock jet is a 126 unless it's a California model then it becomes a 128.


  10. #9
    Senior Member small's's Avatar
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    Pretty sure he has a pre 01 bike. Stock is a 114 and he went up one size on the main. A shim sure wont hurt it. You might notice a little difference. Ive had the 07 a tad over 6,000' with one shim and a 130 main with no problems at all. Im currently running a 126 main which is stock and one shim. I did that for the Utah trip and havent changed it back.
    Last edited by small's; 01-26-2014 at 01:38 PM.

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