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  1. #1
    Senior Member GHDave's Avatar
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    Missing at Higher RPM's

    Hi All! I'm rather a newbie at working on bikes. I've learned a ton on here, but I've not delved into carburetors much yet.

    My wife's TW was bought used last fall. It's a 2007, with about 4600 miles. Oh, and we live at 8200 feet. This machine recently had the First Gear Problem, now solved. Now that she's operational again, I find that she's missing at higher rpm's, notably under load. The mechanic that solved the first gear problem cleaned the carb. I have tried changing the plug (seemed to help a bit), leaning the pilot screw some (ditto) and removing the petcock and checking the screens, which were very clean. The mechanic said he didn't find a lot of crud in the carb.

    My 2013 (bought new) runs well with nothing having been changed, carb-wise. I surmise that the too-lean original setting is offset by the elevation at which I live. I have read qwerty's post on Carb Tuning.

    So, my questions: Do I set out to change the main jet, or do I continue to tinker with the pilot jet? (BTW is there a good tool for adjusting that on the bike? The stubby I ground down to use is so clumsy that I'm afraid to run it all the way in for fear of damaging something.) If I'm going to change main jet, any suggestions as to size(s) I should try first? Or, third possibility, are there other things I should be checking before tinkering further with the carb? Lastly, many people suggest shims, and qwerty discusses them, but it's not entirely clear to me where they go.

    I could go back to the mechanic, but I'd much prefer to learn how these things work, if I can.

    Any suggestions greatly appreciated, ideally expressed in a TW Carbs For Dummies manner .

  2. #2
    Senior Member RockyTFS's Avatar
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    Well, the first thing to figure out is if hers has the same main jet size as yours. Both bikes would normally have a 126 main jet. My 2010 has a 126 and the only time I change to a 122 is when I plan to be above 8,000 feet for a few days. The pilot jet has little effect on the mixture above half throttle, so that is probably not it. I set mine at 2 turns and never changed it. I live at 5,700 and normally ride between 4,000 and 9,000.

    I HAVE experienced missing, or I would call it stumbling, which is a little more subtle than a real miss, at full throttle going up hills. It is intermittent, and never occurs in any lower gear than 5th. IF I lived in Nederland and NEVER went all the way down to Boulder, I would probably leave the 122 in all the time. Problem is, coming up the canyon, you are going to be too lean winding it out to avoid being run over! ( Boy, I LOVED that road!) The 126 is just right from 4,000 to 7,000, and will work all the way to 12,000, but not WOT in 5th.

    One thing to check is get her bike to missing at full throttle, then cut the throttle, clutch in and coast to a stop and pull the plug. If it is pretty dark, the carb is too rich. If it is an ignition problem, the plug will look fairly normal. Ignition problems almost always get worse under heavy load. A 2007 should not have any ignition problems at 4,600 miles, this is pretty rare on the newer bikes, so I think it is much more likely to be cab related.

    As for your stubby, I'd grind it a bit narrower so you don't bugger the threads in the hole. If you loosen the clamps, you can turn the carb up to 40 degrees to the right without having to detach the throttle cables. Then you can see what to do.

    At the time you DO decide to remove the float bowl, get some JIS screwdrivers FIRST! Then replace all four bowl screws with SS Allen head bolts. Or you could take in in and ask the mechanic to just loosen the screws (provided HE has JIS drivers!) so you can replace them. This will make jet changes a piece of cake. Have a careful look at the carb pictures before and during a jet change...parts can fall out! You want to hold the main jet holder with one wrench while unscrewing the jet itself with another, that way nothing will fall out. You will not need to remove any other parts to do a jet change, just make sure the gasket is seated in the bowl recess, and only tighten the Allens moderately with two fingers.
    TWilight and mhomadness like this.
    Rocky
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  3. #3
    Senior Member GHDave's Avatar
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    Thanks for your thoughts, RockyTFS. It sounds like you have some local knowledge. I'm not in Nederland but almost as high, and I do ride up and down a canyon to go to Boulder.

    The miss is in second or third too, at or near WOT. I've just gone 8-10 miles since I changed the plug, to an "Irridium" one sold by ProCycle. I'll have another look at it.

    I did grind the stubby pretty narrow, and a little while ago I cut off the handle so it fits in more easily. And a dentist-type mirror from O'Reilly helps. Also, being a faithful reader of this forum, I bought some JIS screwdrivers awhile ago. And I've got an order building at Bolt Depot anyway, so added some replacement stainless socket cap screws to it. At Bolt Depot they're 9¢ each.

    I'm wondering if the carb was cleaned and reassembled properly. Looks like I'm going to need to tear into it, and try changing main jets. (By the way, if I may display my ignorance further, what the the numbers of jets refer to? The size of the orifice, or just an arbitrary index number? And how do you tell what number one is - are they stamped or something?) Sounds like I might be able to get some help from Rockytrail, who only lives a few miles from me.
    Last edited by GHDave; 05-26-2015 at 06:21 PM.

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    Senior Member jb882's Avatar
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    I take it this bikes engine recently came apart to fix the other issue? And this is a new symptom and not present before? If so i would check the cam timing, if its off one tooth it will cause the exact issue you are describing aty high rpm, a hard skip like the motor is missing. Its pretty easy to check, the procedure is in the service manual that's available on this site. Its pretty simple and only requires a few tools and no major surgery. If its off id bet cash that its one tooth's worth to the right on the cam timing mark. If it is off id make the guy that blundered it fix it.
    Last edited by jb882; 05-26-2015 at 06:34 PM.
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    Senior Member Leisure Time Larry's Avatar
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    A 125 main was in some bikes... might be what you need. Here are part #s that I have for main jets:

    288-14355-61-00 = 122
    288-14355-62-00 = 124 [AKA 288-14343-62-00]
    288-14343-63-00 = 125
    288-14355-63-00 = 126
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  7. #6
    Senior Member RockyTFS's Avatar
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    Quote Originally Posted by GHDave View Post
    ...... (By the way, if I may display my ignorance further, what the the numbers of jets refer to? The size of the orifice, or just an arbitrary index number? And how do you tell what number one is - are they stamped or something?) .....
    They are arbitrary numbers, but the bigger the number the bigger the orifice. The Yamaha OEM jets are stamped, but you will need a magnifier to read it. Best to go by Part Number from Yammie or ProCycle.

    As far as an improper reassemble, it is unfortunately very common, unless the tech has considerable TK specific knowledge. First things first: verify the jet size. Don't just change it arbitrarily....why would her bike stumble and yours not if they had the same jet?

    One other thing you can do before opening up anything is just run two tankfulls of SeaFoam through hers and see if anything changes.
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    Rocky
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    Senior Member elime's Avatar
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    Quote Originally Posted by GHDave View Post

    The miss is in second or third too, at or near WOT.
    Get a brand new jet of what ever size is in there now and start from there. Twice it cured my problem -- in two different TW's, and once in a friend's TW.

    No matter how good the existing jet looks, get a brand new one.
    Last edited by elime; 05-26-2015 at 10:10 PM.
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    Senior Member GHDave's Avatar
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    Quote Originally Posted by jb882 View Post
    I take it this bikes engine recently came apart to fix the other issue? And this is a new symptom and not present before? If so i would check the cam timing, if its off one tooth it will cause the exact issue you are describing aty high rpm, a hard skip like the motor is missing. Its pretty easy to check, the procedure is in the service manual that's available on this site. Its pretty simple and only requires a few tools and no major surgery. If its off id bet cash that its one tooth's worth to the right on the cam timing mark. If it is off id make the guy that blundered it fix it.
    Actually it was running kind of rough before the infamous first gear problem, which is why I had the mechanic clean the carb while he had it off. The guy is (or at least claims to be) a factory-trained Yamaha mechanic, and seems a really nice, straightforward guy. I suppose anyone can make a mistake, but it seems unlikely in this case. I have the service manual, so maybe I should check that.

  10. #9
    Senior Member GHDave's Avatar
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    Quote Originally Posted by RockyTFS View Post
    They are arbitrary numbers, but the bigger the number the bigger the orifice. The Yamaha OEM jets are stamped, but you will need a magnifier to read it. Best to go by Part Number from Yammie or ProCycle.

    As far as an improper reassemble, it is unfortunately very common, unless the tech has considerable TK specific knowledge. First things first: verify the jet size. Don't just change it arbitrarily....why would her bike stumble and yours not if they had the same jet?

    One other thing you can do before opening up anything is just run two tankfulls of SeaFoam through hers and see if anything changes.
    Can I make an assumption as to which jet is in my 2013, bought new? The 126, right? I can't say that the 2013 has the perfect jet, not having tried any others, but it runs smooth.

    I've been running SeaFoam through, but only the maintenance dose of about 1 oz per gallon. What dose would you suggest I run through? I don't know if we've even run an entire tank through since we've had it, what with winter arriving shortly after its acquisition and the cursed cool wet spring we've had.

  11. #10
    Senior Member RockyTFS's Avatar
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    Quote Originally Posted by GHDave View Post
    Can I make an assumption as to which jet is in my 2013, bought new? .........cursed cool wet spring we've had.
    Yes, the 126, if bought new and never messed with. WET? I have now measured SEVEN inches of rain in May and we got three days to go!!!

    I'd run two tanks at 2 Oz. per gallon and see if it makes a difference on her bike.
    Rocky
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