Hi,

I was hoping someone with a bit of XT carb knowledge could help me.

I've got a 2002 XT600e. It runs fairly well at sea level, but appears to have a slight mixture problem that gets worse at high Altitude.

Symptons:
At sea level, with a wide open throttle, it accelerates cleanly, but closing the throttle quickly results in a small lurch (No big problem)

Above 1000m (3000ft), it starts struggling on load. If too much throttle is given under load, it will "chug" and falter, and backing off the throttle results in it smoothing out. At higher heights this gets much worse, so the barest throttle opening results in the bike losing power and faltering, leaving me crawling up hills at 30mph.

I suspect this is because the mixture is too rich, made worse at higher altitude with less dense air. The iridium spark plug appears normal in colour and deposits.

Reading the archives, people have mentioned a notch on the carbs right hand side. Could someone please explain in laymans terms clearly how to lean out the mixture a little so I can have a few horses back as it is not immediately obvious what to do!

Any help or suggestions would be very much appreciated.

Will
XT600e (In line fuel filter. 23ltr Acerbis Tank
San Jose, Costa Rica.

If the carbs are still original, no jet kit or tuning along the way, I would make sure the air filter is clean and also check the choke to make sure it is closing completely.

Do you have a picture of the 23 ltr tank on your bike? Of a link to a bike with the same tank?

Hi, thanks for the reply. Air filter is new, OE spec, and can breath freely. Choke is not sticking as far as I can tell - At altitude it never needs it either.

Details of the bike / tank for your reference can be seen at www.Wrongwayround.com

Thanks,

Will

I know these things don't really relate to running rich but they're easy things to try.
Maybe water in the fuel? Have you tried draining the float bowl?
Have you tried swapping the ignition boxes on the bikes to eliminate that?
How about the vent tube that comes off top of the right hand carb and runs under the seat, is the filter clear? Hose not pinched?

Make sure all the little hoses on the carbs are clear. If the float bowl doesn't vent it can affect mixture.

After you drain the float bowl, take the plug off the bottom of the right-hand carb, make sure the main jet has not come un-screwed. With the plug out, turn on the gas briefly and make sure plenty of gas flows to the right-hand/secondary carb.

I can't think of any other things to check without removing the carb. You can lean out the pilot screw with the carb on the bike but that only changes the mix at idle to 1/4 throttle or so, I can't see how that would help your problem.

From your travel itinerary it looks like you want to leave town about now. If the little things don't clear it up, I would be tempted to pull the carbs and go through them to make sure there isn't a loose jet or needle clip.

Has this problem been coming on slowly or did it start all at once?

Thanks Forschmiedt, there's plenty of stuff for me to try.

It's a good point about swapping the ignition units with my friends bike. One thing I should have mentioned is that Matt's bike suffers in exactly the same way, same traits, same symptoms, but not as dramatically as mine - Again, his XT600 4PT 2003 gets progressively more hesitational and throttle sensitive as we climb altitude

His symptoms are not as bad, and he gets about 5-10% better fuel economy than me (and he weighs more )... So maybe he is running leaner. However, his XT consumes more oil, maybe 1 litre every 2000 miles, compared with 0.2 litres or so for me.

I'm not sure if this helps with diagnosis, but it was probably worth mentioning just in case.

With the fact that Matt's XT show similar traits, maybe we should have brought out a replacement needle kit for higher altitudes....

I agree that the mixture adjustment for idle / 1/4 throttle will probably not help me very much (but maybe worth a try)...

It first starting appearing in the Sierra Mountains in Mexico, the first high altitude point of our trip. It is DEFINITELY altitude related - Since then we've done 7000miles, and climbing/falling 1000's of metres in a matter of hours and the difference is very noticeable, to the point that I can tell our altitude from the XT performance almost as precisely as looking at the GPS

Thanks again!

Will

[This message has been edited by dionysos (edited 05 September 2005).]

Both bikes, eh? I was assuming it was only one bike and trying to think of things that may be wrong with the bike. If both are acting similar, I wouldn't be trying to find problems, I guess. I'm a bit surprised you're having that much trouble at 1k mtrs. I wouldn't expect big problems until closer to 2k mtrs.

Without spare main jets, you aren't going to be able to lean them out at full throttle, the way to do that is put in smaller jets. You may be able to drop the needles a notch or two if they are the type of needles that have more than one groove. That will at least give you 1/2 to 3/4 throttle a bit better.
Considering that it's a bit of a pain to get the carbs out of these things, that won't be fun.

How is the quality of gas? Have you had any crappy gas problems in any of the countries you've been through? For the bikes, not from the food.

Try to adjust the carbs for an altitude of 500 or 600meters.. but try to see if you win in performance but don't loose too much in litrs/km or gallons/mile or wathever... do that if your gonna go to the mountains if you want to of course oh, and there's nothing better as a new sparkplug... I personally use the DPR8EA-9 [1990 XT600E] and make sure it is tighten enough because if it does get a little loose you will loose power I know because it happened to me :P

Happy riding!

Hi Will,
For what it's worth - I was chatting to one of the guys at Metal Mule Luggage recently, he has toured extensively on an xt 600E which is currently buried under an enormous pile of many things bike related, he mentioned that the XT loses 10% of it's power for every 1000ft of altitude because of the reduction of pressure/oxygen. He was particularly excited about the prospect of the new Tenere which is fuel injected and adjusts the mix to compensate somewhat for the effects of altitude ( but not entirely ). So it sounds like your bikes are OK but on " go slow " when high up !
cheers Mike

They only define the mix at full throttle, and since you are travelling, and not racing, this is totally irrelevant.
Indeed, your two bikes run rich, caused by the lower air density at altitude. I just guess that the problem is more in the 2nd carb than in the first one because it is Yamaha's second carb that is set pretty rich as standard for performance and to keep things cool at higher engine loads.
If you ride for extended periods of time at altitude, you can lower the needle of the second carb one (try, maybe 2) notche(s). This will lean out the mix at larger carb openings. BUT BEWARE! Returning to sea level, return the needle to it's original position!
Leaning out too much will cause hesitation and occasional hiccup, then it is time to return to a richer stetting.

Good luck!
Auke

__________________
Auke
http://aukemarieke.blogspot.com

Good day Aukeboss,
I just wanted to say that your technical advice when I had some problems with my TT600R a few months ago was very much appreciated; I know that I will have said this at that time - the reason that I am raising it again is because of another thread in here about the XT600 thread Vs a thread for Yamahas in general. I guess you may have read it already.
I would like to know your views on the opinions that have been expressed in there so far.

http://www.horizonsunlimited.com/hub...bout-yam-29080

I notice here that you are still picking up on XT technical problems/questions (and providing sound, practical advice) even though this techie forum has changed title recently.

For motorbike mike and bacardi23: the original question that you have answered is 2 years old - I hope that dionysos is still not adjusting his carbs in Costa Rica!
Oh well, what goes around, comes around, especially when it relates to engines running lean at altitude.

__________________
Dave

Actually, I have had the question why it is called the XT 6 forum already for a long time, but I'm more a result person than an appearance person.
Meaning, if people can get their advice, ask their questions, what's wrong? So, for me Yamaha or Yamaha XT forum, all the same.
Note that I formally do not belong to the XT6 site; as I'm in the possession of a Tenere and a TT, both not being an XT600 to purists. Just imagine that I have been lurking on this site while in the possession of a CDI ignited bike iso the TCI ignited XT6 ..... to name a few differences.
Deep in my heart - if you think 'travel bike' and 'Yamaha' it must be an XT in some form: Tenere, TT, XT, so either name is OK.

Seriously, if the new name is what people are happy with, let it be so. I will not stop my solicited and unsolicited contributions ...

Auke

__________________
Auke
http://aukemarieke.blogspot.com

Thanks Auke - a very considered answer and very clear. It is of interest that you do not consider yourself to be part of the "XT" community in here after all of your input to that thread!!

I had thought that you would post on that other thread; I will link across because Grant is still listening to opinions on this.

Regards,

__________________
Dave