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My mechanic, a past Yamaha dealer and friend, now working in his back yard has spent much time trying to figure out the mystery of my choke killing the engine cold or hot. In case anyone else has experienced this problem, here is what was finally discovered. My TW is an '06 model that had 605 miles on it when I purchased it during the summer of 2012. It was delivered by a friend of the owner who may have been the one who screwed up the carburator big time. The owner claimed it ran great before delivery from a town north of me. When received it would only run with the choke on, but ran pretty good in fact. I was not inclined to continue riding with this condition in effect. So, delivered bike to my mechanic for carb cleaning which he did along with replacing the pilot jet which someone had broken the screw driver end. After this work, the TW ran just fine except for two things....Choke now kills the engine and it runs a bit lean causing detonation on hard excelleration. More searching and work looking for a solution to the choke mystery. Finally he discovered that a small aluminum plug had been removed from a place not designed for the choke (enrichener) to take up fuel, but it would if the plug was removed. This caused the choke to have no metering and it just flooded the engine every time it was used. Problem solved, hole plugged and choke works nicely now, but seems to cause the engine to idle somewhat fast when choke is on. Have only ridden the TW 225 ft from the trailer to my shop, so do not know if all is right. But, my mechanic rode it and is satisfied with it's performance. Hope this scenerio will be helpful to someone having the same problem.



UPDATE:

Forgot to mention that the mechanic placed one shim under the needle while fixing the choke. Now the engine does not detonate at 50 mph under hard acceleration. It also pulls better and overall runs better. I have ridden it over 20 miles since the choke fix and needle mod. What a pleasant bike to ride....well pleased with it now. Many thanks to all that contributed to this thread....Dan
 

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The bike will idle faster when choked, that sounds normal to me. I hope you have it sorted out so the fun can begin!
 

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When I say fast, it is very fast, not destructive fast, but a little uncomfortable fast. Don't know how to slow that down. Wonder if others idle very fast with the choke on the first notch?
 

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When I say fast, it is very fast, not destructive fast, but a little uncomfortable fast. Don't know how to slow that down. Wonder if others idle very fast with the choke on the first notch?


Both mine idle pretty fast with the choke pulled all the way out. I don't feel comfortable leaving it at that RPM very long but since they warm up pretty quickly I don't need to leave the choke all the way out very long.
 

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When I say fast, it is very fast, not destructive fast, but a little uncomfortable fast. Don't know how to slow that down. Wonder if others idle very fast with the choke on the first notch?
Yes, the choke makes it idle faster. You should only need it on a cold start.



That hole inside the carb you mentioned, is supposed to have a rubber plug in it.



If someone tried to clean the carb passageways with compressed air, the plug can easily go "flying" and never be seen again.



Jb
 

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sounds to me like you got it back to acting as it should (stock). If you read up on the idle air mixture modification, you'll probably find you don't need the choke any more. Easy to do, better running, no cost (unless you wanna pay yourself)

TIM
 
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