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Discussion Starter #1
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 :D.
 

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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.
 

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Discussion Starter #3 (Edited)
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.
 

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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.
 

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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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...... (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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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.
 

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Discussion Starter #8
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.
 

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Discussion Starter #9
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.
 

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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.
 

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I had a similar problem with my Tdub after it sat for a while. I assumed that it was carb related, and after going through the carb the problem was still there. How is your battery. Sometimes the smaller bikes do not make enough electrical power to run at WOT. They relay on some battery power to help them during WOT, then recharge during normal operation. I changed my battery, and the problem magically went away.
 

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Discussion Starter #12
I had a similar problem with my Tdub after it sat for a while. I assumed that it was carb related, and after going through the carb the problem was still there. How is your battery. Sometimes the smaller bikes do not make enough electrical power to run at WOT. They relay on some battery power to help them during WOT, then recharge during normal operation. I changed my battery, and the problem magically went away.
That's a new one I'd not heard. Is there an effective way to load-test a battery, or does one use the replace-and-hope method?

BTW this morning I'm going to see a forum member that I've not met, but that lives a couple of miles from me, to see what we can do.
 

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Discussion Starter #13
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.
I'd be interested in how a jet could fail, assuming it's not clogged. It's a piece of brass, what could go wrong, unless some bonehead drilled it out? But then, it did work for you, so it looks like that's the next thing I'll try. I took it apart today, everything looks good, and there is a 126 in there. Unfortunately I did this at Rockytrail's house, a few miles away, and didn't have any new jets on hand, so had to reassemble it as is. There doesn't seem to be much doubt that it's running rich.
 

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Discussion Starter #15 (Edited)
OK, next problem: I can't find a 126 jet online. Part 288-14355-63-00, shown in several places on the forum as the right part number, is "Not Available" or not found at Partzilla, Rocky Mountain ATV, Stadium Yamaha, Ron Ayers , Boats.net. SpeedSupplies,com says "Not Available - Obsolete". Online chat guy at Partzilla says that part is no longer made, but was zero help as to a replacement.

So, does anyone know how to get a 126 jet for a 2007? Is there a replacement part number? None of the fiches show a 126, though there are 125's and 128's. If I can't find one I guess I'll try a 125.
 

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Discussion Starter #16 (Edited)

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GHDave, you should just get the #125 jet. Elevation is one of your issues, well the smaller jet will only help that. The #125 went in some bikes, the #126 went in some bikes...not a big deal. I quickly looked on Rocky Mtn, and for the 2015 TW200 the diagram lists the #126 main jet, part# 5FY-14343-63-00. They sometimes change up or have different part #s in different catalogs. I'll update my records. You may also want to add a #122 & #124 to your order.
 

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Discussion Starter #18 (Edited)
lrppcer, thanks for the info! Ordered a 125 & a 126. I hope my situation turns out like elime's. If changing the jet doesn't work I'm not sure what I'll try next. As an old friend used to say, I'll burn that bridge when I come to it.

Side Note: I called Colorado Powersports, the Yamaha dealer in Boulder (where I bought my 2013 TW new, but I'm sure they don't remember that), to see what they had. They have a "Parts Finder" on their website, which showed the 125. I called, talked to the parts guy, and was told they had them in stock, just under $5. Further perusal of their "Parts Finder" showed they had the 126 as well. So I drove down there. "No, we don't have any of those. The website doesn't show actual inventory." And the guy who told me they were in stock? "Who did you talk to?" Of course I didn't remember who I talked to. That was the first and probably the last time I try my local shop for parts.
 

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....... Is there an effective way to load-test a battery, or does one use the replace-and-hope method?.....
Yes, a load tester, which many dealers have, will give you an idea. From your description of your dealer, you may be better off to just use a voltmeter at home! Check the voltage, leave the lights on for 15 minutes, and test again. Record that number, wait half an hour with everything off, test again. The voltage should recover to nearly the initial voltage. If the battery is bad the lights may not even LAST 15 minutes. :eek: Small motorcycle batteries are doing well to last three years. However, a battery that will crank the engine enthusiastically and repeatedly when it's only run for a minute or less is in pretty good shape...that is another simple field test.

As far as main jets, they can corrode in situ, most likely from letting Ethanol fuel sit in the carb for lengthy periods in a humid climate. It's really impossible to see in the orifice, but if the outside is corroded it should be replaced.
 
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