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carb adjustment for altitude carb adjustment for altitude
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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
Photo by George Guille, It's going to be a long 300km... Bolivian Amazon

I haven't been everywhere...
but it's on my list!


Photo by George Guille
It's going to be a long 300km...
Bolivian Amazon



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  #1  
Old 18 Jan 2003
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carb adjustment for altitude
Can anyone advise on carb adjustment likely to be required on XTZ660 carb (twin choke Teikei same as XT600) at altitudes of 3000 - 5000 m? How sensitive are these carburetors to altitude change? Is dropping the needles to top groove likely to be enough or will main jet changes be required? Has anyone tried lowering the float level as an alternative to jet changes?
thnks
shaun
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  #2  
Old 20 Jan 2003
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It all depends also on your exhaust and air filter. A standard 660 has a very rich mixture. The first thing to do is either drill a hole in the exhaust damper end pipe or mount an other exhaust, and mount another air filter like K&N. This is reasonably ok for sea level. If you want to mess with the carb, try a smaller main jet in the 1st carb, say 124-126 instead of the standard 130 [this is for 3YF models 91-94]. I have 122 which is standard for newer models, in combination with a lifted needle in the 1st carb. by 1 pos.
For mountains upto abt. 2200 m. you can drop the needle in the 1st carb by 1 pos.
I have no experience with higher altitudes.
Remember that measuring on a test bench is always the best.

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Fred, XTZ660, Holland.
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  #3  
Old 21 Jan 2003
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Thanks Fred, bike has a K&N filter and Micron exhaust but still with standard jetting, (130 in first carb), so should be running a bit leaner than std already.

Quote:
Originally posted by FredXTZ:
It all depends also on your exhaust and air filter. A standard 660 has a very rich mixture. The first thing to do is either drill a hole in the exhaust damper end pipe or mount an other exhaust, and mount another air filter like K&N. This is reasonably ok for sea level. If you want to mess with the carb, try a smaller main jet in the 1st carb, say 124-126 instead of the standard 130 [this is for 3YF models 91-94]. I have 122 which is standard for newer models, in combination with a lifted needle in the 1st carb. by 1 pos.
For mountains upto abt. 2200 m. you can drop the needle in the 1st carb by 1 pos.
I have no experience with higher altitudes.
Remember that measuring on a test bench is always the best.
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  #4  
Old 2 Mar 2003
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I've got the same question as Shaun but for an XT600E. Is it required to intstall a smaller mainjet for high altitude driving (KKH)? If so, which type? I hoped lowering the needle and taking the top of the airfilterbox will be enough?
cheers
Bart
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  #5  
Old 3 Mar 2003
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The main jet is only used at Wide Open Throttle. What you will mostly be using in the mountains is between 1/4 and 3/4 open, where the mixture is set by the needle. You can note when the mixture is too rich that the engine doesn't easily pick up on accelerating and sounds like an Opel GSI instead of a Toyota Corolla GT Twin Cam.
What is KKH?
I wouldn't take the top off the box because 1) it doesn't help
2) you collect dirt and/or water
Have you already mounted a K&N air filter?
Have you already modified the exhaust?

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Fred, XTZ660, Holland.
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  #6  
Old 7 Mar 2003
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Hi Fred
thanks for the info.
KKH = Karakoram Highway
I haven't made any modification yet as I'm first trying to find out which modifications are absolutely needed. Prefer to spend my money during the trip ;-)
Do I have to do any other (carburator-)modifications if I install a K&N filter?
Any idea how this influences fuel consumption?
Has someone experience with high altitude driving on a standard XT600E?
cheers
Bart
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  #7  
Old 10 Mar 2003
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Ha Bart,

you don't have to change anything when you mount a K&N air filter.
Fuel consumption should be less, if you don't get tempted to use the extra bit of power all the time.
Which model XT600E do you have?



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  #8  
Old 11 Mar 2003
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Hej Fred
that's good news. A modification worth to consider.
My XT: model 2002. Haven't got the bike or papers yet so no idea about right description.
Bart
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  #9  
Old 11 Jul 2017
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Hi Fred,

Im in Dushanbe with my XTZ 660 (year 94) and want to do the Pamir. On the way here I noted that on 3200m the idle is very low and the bikes switches off. Id like to modify t for the Pamir (4000m) and I got already another airfilter (washable but not sure if k&n though). If drilling a hole in the exhaust damper end pipe works, then I would do that, but Id need some better info where exactly and how big. Also what are your thoughts about the high altitude road? Doable? ..when I had the low idle/switch off problem, I held the throttle more open.

Any help is welcomed!!

Happy trails!

Markus
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  #10  
Old 11 Jul 2017
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Pamir with an XTZ 660
any idea what will happen when trying with current setup? I tried to find specs for max altitude and if someone ever did it on the same bike.. didnt find anything though
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  #11  
Old 11 Jul 2017
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I did not do any adjustmend. My 125cc Honda was very slow on steep roads high up in bolivia but normal speed on strait roads. You cant destroy a bike with tooo much petron but if you burn to less inside the cylinder when going down to normal altitude it will get to hot. This way you can wrack your engine: Offroad Motorrad Weltreisen - das letzte Abenteuer
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  #12  
Old 11 Jul 2017
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Remove the snorkel from the airbox, and adjust the CO screw underneath the primary carb. That should help a lot
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  #13  
Old 11 Jul 2017
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Quote:
Originally Posted by Jens Eskildsen View Post
Remove the snorkel from the airbox, and adjust the CO screw underneath the primary carb. That should help a lot
CO screw? It wont do much good adjusting this cause its only for low rpm, screw adjust the fuel amount in the main carb.
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  #14  
Old 12 Jul 2017
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And the new poster talked about low idle, stalling ect. Adjusting the CO screw should fix that right up.
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  #15  
Old 15 Jul 2017
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Thanks for the advice! ..haven't reached 4000m+ so far, but will give it a go with removing snorkel.
Bumpy roads here and breathtaking views after every bend!
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