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Discussion Starter #1
I've recently noticed development of a single sputter and stumble on my '07 when I roll on the throttle while cruising in third gear and sometimes in first on takeoff. The bike sputters, stumbles then accelerates when this occurs. I'm running with a 130 main jet, 4 shims on the needle, pilot screw 2 & 3/4 turns out and the bike was running STRONG till now. I just pulled the snorkel last night hoping to give her a little more air as I'm pretty sure she's running rich once this stumble developed. I was thinking I should back off 1 shim and see what happens but I know you guys know a lot better than I do so here I am. Should I be concerned about any other possibilities here? What would you guys recommend me trying? Thanks all, I know I can get this straightened out quick with your collective help and extensive knowledge, good to be back! Hopefully I'll have a hollow mod pictorial to come soon if time allows!
 

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First thing to figure out is why it's running rich all of a sudden. Did you check the plug to verify? Smoke from the exhaust? Change source of fuel? Air filter dirty?
 

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If it ran strong then developed this symptom, something changed. Plug, fuel supply, debris in the tank or within needle valve inlet, type of fuel, or change in temperature/humidity/low pressure/etc. How long had it been running strong? Any noticeable environmental changes? New gas station?



I'm making a big assumption that the shims are 0.010" but, if so, bring it down to 0.030". You may actually be running fat until the air can catch up to the fuel.
 

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Discussion Starter #7
First thing to figure out is why it's running rich all of a sudden. Did you check the plug to verify? Smoke from the exhaust? Change source of fuel? Air filter dirty?


Plug tip was actually wet and dark when I pulled it, definItely running rich. I know my air filter definitely needs cleaned so I'll get on that, I dropped 1 shim off (total of 3 on now) and I'll turn the pilot in 1/2 turn from nearly 3 out. My fuel source is fine and the same, no exhaust smoke, I've been running rich for a while now I suppose. I'll ride a bit tomorrow and see how she's responded to the change, stay tuned for a swift update and more questions for you. LOL Thanks for all the response fellow Dubsters <--- (I'm coining that term)
 

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Discussion Starter #8
First thing to figure out is why it's running rich all of a sudden. Did you check the plug to verify? Smoke from the exhaust? Change source of fuel? Air filter dirty?


Hey Qwerty, so I dropped to 3 shims, turned pilot in to 2 1/4 turns out and the 130 main is still in place. I cleaned my air filter, did a valve adjustment, got new gas in the tank and changed my oil. Still suffering from this stumble. I figure I've been running it rich for some time now, I've never cleaned the carb on the bike yet, I've had it since '08 bought new and I've got 4k on it. should i drop down to the 127.5 I have and clean the carb out? When winter hits I always run it dry, add stabil then run dry again before I store for the winter. What should be my next move at solving this?
 

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Hey Qwerty, so I dropped to 3 shims, turned pilot in to 2 1/4 turns out and the 130 main is still in place. I cleaned my air filter, did a valve adjustment, got new gas in the tank and changed my oil. Still suffering from this stumble. I figure I've been running it rich for some time now, I've never cleaned the carb on the bike yet, I've had it since '08 bought new and I've got 4k on it. should i drop down to the 127.5 I have and clean the carb out? When winter hits I always run it dry, add stabil then run dry again before I store for the winter. What should be my next move at solving this?


1 vote for carb cleaning. If it ran well with this jet before, leave it.
 

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1 vote for carb cleaning. If it ran well with this jet before, leave it.


+1



Clean it all. Use compressed air to blow any debris back out the ports within the carb. Don't forget to take the slide out, clean its sides up (recommend soapy water as it's plastic and not sure on the strength of carb cleaner you have), clean the needle, clean the diaphragm (soapy water again is needed for it's rubber) and make sure diaphragm seats properly before re-assembly. Also make sure spring is seated properly. When done use your finger to slide the slide and make sure there is no obstruction.



Oh and check for cracks on the carb boot, just to be safe.
 

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If it ran well before, and doesn't run well know, and no major environmental changes, something is wrong. Find and repair the defect.



If you stored it with E10 in the tank, that could be the problem. E10 does not store well no matter what you use to treat it. Did you dump the fresh gas on the old gas or drain the tank and start over?
 

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Discussion Starter #12
If it ran well before, and doesn't run well know, and no major environmental changes, something is wrong. Find and repair the defect.



If you stored it with E10 in the tank, that could be the problem. E10 does not store well no matter what you use to treat it. Did you dump the fresh gas on the old gas or drain the tank and start over?


Criminy, I don't even know what E10 is! lol Unleaded 87 octane is what I fuel up with, added stabil to a full tank of fresh gas and stored for no more than two months during winter. When it warms up I fire her up and run on that same stored tank of gas. I had read that the stabilizer was fine to use and that you could just run on it when done storing. I just googled E10 and I honestly still can't tell you if it's ever been in my tank or not. From the looks of it I'll be doing a full carb cleaning and I think I'll just pop in the 127.5 main while in there then do some plug chops and see if I get a better mixture. BTW, What exactly is "popping back through the carb? Cause I suspect I've got that going on but not sure exactly. It's nice to be somewhat mechanically inclined, somehow at the same time I don't know what I'm doing. <---- Make sense?
 

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Not sure if you have a fresh tank of gas in it yet, but from my own personal experience; after winter storage with stabil in fuel, TW ran as you discribed in your first post. Thought I had a carb problem, but discovered when I filled up with a fresh tank of gas, problem gone. Food for thought!
 

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Discussion Starter #14
Not sure if you have a fresh tank of gas in it yet


Yeah, I've ridden it all Summer. Gone through plenty of fresh tanks, I'm thinking it's just due for a good carb cleaning and possible rejetting I'm not sure. Is there a common main jet for the TK carb that people end up happy with? I feel like it ran great with the 130 but at the same time it was apparently running rather rich.
 

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Actually, I don't think Yamaha sells a #127.5 main jet. I'm thinking you've got some oddball aftermarket part that may or may not coincide with Yamaha's jet numbering system. You're on your own when you use oddball parts.



E10 is gasoline with up to 10% ethanol content. Nasty stuff in the real world, because the "up to" part means it can be 10%, 0%, anywhere in between. I've even tested some E10 that was 20%, presumably because whomever mixes the stuff sniffed too many fumes and dropped in a double dose. The varying ethanol contact can make jetting impossible as ethanol requires about half again as much volume for a good air/fuel ratio compared to gasoline.
 

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Discussion Starter #16
Actually, I don't think Yamaha sells a #127.5 main jet. I'm thinking you've got some oddball aftermarket part that may or may not coincide with Yamaha's jet numbering system. You're on your own when you use oddball parts.


The 127.5 is a Mikuni jet, I'm gonna pick up some other Yamaha
jets though and try a few sizes out while I'm at it.
 

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Get a new spark plug, too, and gap it. Never know.

Clean the carb.



If you're not stumbling at high-rpm, wide-open throttle then play with the mid-range jetting rather than the main jet. Don't rejet the main if your high rpm is fine. Everything you said so far says when you get on the throttle, not when holding at high-rpm throttle.



Or, return everything to stock. Does it stumble at stock settings? Then chase the real problem, not the jetting. If it doesn't stumble at stock settings then make one change at a time. When it stumbles again, you've pinpointed what is causing it.
 

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Discussion Starter #18
Get a new spark plug, too, and gap it. Never know.

Clean the carb.



If you're not stumbling at high-rpm, wide-open throttle then play with the mid-range jetting rather than the main jet. Don't rejet the main if your high rpm is fine. Everything you said so far says when you get on the throttle, not when holding at high-rpm throttle.



Or, return everything to stock. Does it stumble at stock settings? Then chase the real problem, not the jetting. If it doesn't stumble at stock settings then make one change at a time. When it stumbles again, you've pinpointed what is causing it.


I'll clean the carb out, button her back up and see if the problem is still there. If it is then I'll drop a shim and test etc etc. It definitely seems to me like a midrange issue, but if I'm still running rich when it's resolved shouldn't I still dial her in for a better mixture after all?
 

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If it was running fine, and now it isn't. Something is wrong. You can't tune wrong. Fix first, then tune, starting with the main jet.
 

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If it was running fine, and now it isn't. Something is wrong. You can't tune wrong. Fix first, then tune, starting with the main jet.
 
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