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Discussion Starter #1
New to the TW world, just bought 2 2018's, one for my wife and will be storing the other for one of my brothers. She's transitioning from a cherry '94 XR200r. Anyway, I looked in an online manual and saw nothing about jetting for altitude. My Honda XR manuals and my son's KTM manual all have the jetting specs to use depending on temp and altitude you're riding at. It gives the needle clip setting, main jet # and pilot jet setting. Does this not exist for the TW's or did I just not see the right manual? Will be riding in Colorado around 10k'. Thanks
 

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Welcome!
Correct, no formal published specs for altitude corrections from Yamaha.
From the factory there is a brass cap on bottom of carb hiding a mixture screw usually set very lean around 1.5 revolutions with lower elevation folks often removing plug and adjusting to about 2.5 revolutions from lightly seated.
Whether this has been done or not on your TWs should make a difference in your subsequent tuning for 10,000 ft.
If you don't have the downloadable service Manual yet here is at least a illustrative photo with common terminology.
Depicts the plug and a sheet metal screw to remove it as well as what we refer to as the pilot screw, idle mixture screw, fuel screw, or sometimes just that dang screw. :giggle:

carb.jpg
 

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The above was just a starting point to move forward from, get a baseline we all understand so we give hopefully appropriate advice. Meant to say others who live & ride more extensively at those elevations can give better specific recommendations based on their TW experience.
 

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I am in Colorado and live at 8000ft with stock jetting with no issues. Adjust the fuel screw out to 2.5 turns like Fred suggested.
 

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Discussion Starter #5
Welcome!
Correct, no formal published specs for altitude corrections from Yamaha.
From the factory there is a brass cap on bottom of carb hiding a mixture screw usually set very lean around 1.5 revolutions with lower elevation folks often removing plug and adjusting to about 2.5 revolutions from lightly seated.
Whether this has been done or not on your TWs should make a difference in your subsequent tuning for 10,000 ft.
If you don't have the downloadable service Manual yet here is at least a illustrative photo with common terminology.
Depicts the plug and a sheet metal screw to remove it as well as what we refer to as the pilot screw, idle mixture screw, fuel screw, or sometimes just that dang screw. :giggle:

View attachment 205689
Thank you both very much. In the past, where we ride at 10,000 ft, the XR200 and XR250 struggled, so I started jetting them every year before we headed up and it certainly helped. I ride a 450, so even with a 20% reduction in power, I have more than plenty left, so I never messed with jetting it. I will adjust the idle/air screw, as you stated, and see how it does on the trip in early July. Thanks again
 

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I live mile high and typically ride up to 8,000 or so with the occasional 10,000 and 11,000 ft destinations.
My TW200s are set up stock as Errtu says with exception they both are California bikes. They perform well enough.
 

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Some people alter their air box and add holes they can cover and uncover depending on how high up they are. If you check this forum you should find a few posts covering this.
 

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Just what I was wondering about. I just bought a 2020, and it seems to be running a bit lean. I'm at 3500 ft. I will remove the plug and go from there.
Thanks!
 

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For riding around 10,000 ft elevations I would be very reluctant to increase either pilot jet or main jet sizing.
carb bottom.jpg


Here is stock jetted TW200 carb feeding a TTR225 engine in my Betty Boop as she summits a 11,400 ft peak.
Mixture screw is at 2.25 revolutions and air box has numerous additional holes. Engine sounds a little rich but bike accelerates up into 6th gear at the 11,000 ft level and then still pulls well as gradually downshift due to steepness and looseness of terrain.

 

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I always adjusted the mixture by going lean until the engine started running poorly then back it up one, sometimes two steps and that was usually a really good spot. If you go one more step lean usually the engine wouldn't run at all.

Going to the rich side of things, one can go very rich and the engine will still run though it will slowly get worse and worse as the mixture gets richer and richer, as for example you increases jet size or you gain altitude.
 

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Discussion Starter #13
For riding around 10,000 ft elevations I would be very reluctant to increase either pilot jet or main jet sizing.
View attachment 205764

Here is stock jetted TW200 carb feeding a TTR225 engine in my Betty Boop as she summits a 11,400 ft peak.
Mixture screw is at 2.25 revolutions and air box has numerous additional holes. Engine sounds a little rich but bike accelerates up into 6th gear at the 11,000 ft level and then still pulls well as gradually downshift due to steepness and looseness of terrain.

Thanks Fred, I've done a lot of carb work on a lot of bikes, but that pic with explanation is the best I've ever seen.
 

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Good link NorthernSpy! (y)

JBFLA deserves all the credit for putting together that post with the ever so helpful photos and labels a decade ago.
Occasionally there is something new under the sun but for a bike made since 1987 it should not be a surprise that a few long term owners have been around the block.
The search and stickie functions on Forum can dredge up a vast wealth of information to answer most questions.
 
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