Adjusting for high altitude.

So im moving out of NJ and taking the 650L. Ill be living in colorado at a height of 5000ft as well as taking it into the mountains at 10000 plus. Can I adjust the carb for the altitude myself?

If you can open up a carburetor and change the main jet, then yes.

Jets. Plural.

Jets. Plural.

I don't know about your bike, but MY XR650L only has one main jet.

It has another jet that will also need changing for the high altitude...

It has another jet that will also need changing for the high altitude...

Would that be the pilot jet?

 

I can't think of any others in there.

It has another jet that will also need changing for the high altitude...

Where could I start with that? Im sure I can change the jets, I assume it's a larger set?

The higher you go the richer it gets, becouse the air gets thiner, there is less oxygen than on sea level so you will need leaner jets, so that there were less fuel in the mixture  :)

You usually need to change only the main jet.

It actually shouldn't affect 650cc that much, like it does to 250cc, so I would first try and ride there as it is now, and then if it makes bulb-bulb-bulb sound instead of increasing rpms while going up the hill then the jet needs to be leaner. Also I would just use a piece of wire to make it leaner like I did on 250cc every 3000ft higher so don't listen to me  :D

Where could I start with that? Im sure I can change the jets, I assume it's a larger set?

 

Go to the FAQ at the top of the XR600/650 forum and look for Dave's Mods. It should have a .pdf file linked in there somewhere with illustrated instructions on how to go through the whole 650L carburetor, including changing the jets. There are also numerous threads about doing plug readings to dial-in the mixture.

 

The higher you go the richer it gets, becouse the air gets thiner, there is less oxygen than on sea level so you will need leaner jets, so that there were less fuel in the mixture  :)

You usually need to change only the main jet.

It actually shouldn't affect 650cc that much, like it does to 250cc, so I would first try and ride there as it is now, and then if it makes bulb-bulb-bulb sound instead of increasing rpms while going up the hill then the jet needs to be leaner. Also I would just use a piece of wire to make it leaner like I did on 250cc every 3000ft higher so don't listen to me  :D

 

My experience is the opposite. My bike will start to blubber and load up on the low end (pilot circuit) and become a lot tougher to restart as I go up in elevation, but it clears out a bit and runs better at ~50-100% throttle (main circuit). It picks up power across the board and cleans up a lot at low elevation, leading me to think that it isn't a case of lopsided (rich pilot/lean main) jetting. I doubt it's lean anywhere with 68/170 brass. Also, the more power an engine makes, the more sensitive it will be to air density changes because a small drop in density equates to a larger drop in power and that means a larger drop in fuel demand and, thus, jetting.

 

I've done the wire trick through a jet before, too. :D

Edited by HeadTrauma

I have the 600 and live in Utah, same elevations you're talking about.  I live at 4500 and I ride from there all the way up to 9000 or 10000.  the 600 does pretty good with the varying elevations.  I am running a 160 main and a 62 pilot.  needle position 2nd from the bottom.  I think the needle position is stock as well as the pilot( I forget exactly)  there was a chart in my Clymer manual that showed how to change the stock jetting for altitude.  I came up with about a 10% change in jetting at my elevation which is pretty close to what I have in the carb now.  It runs pretty good.  Honestly, I would ride it at your 5000 feet with the stock jetting and see if it runs rich or not.  If it does, then you can start fiddling with it.  It's tedious, but I would only change one thing at a time.  the suggestion above to start with the main and work down to the pilot is a good idea, never heard it like that before.  that'll create a method to the madness:)

Well, you've still got the idle screw for the idles, if you screw it in fully and it's still rich on idles then you need leaner pilot jet, but this is rarely a necessity   :)

If it's bulb-bulb-bulbing between idles and mids, then you should put the needle lower, else if it doesn't help then mess with different jets

Should start from the simplest things first =)

Edited by MCVL

Go to the FAQ at the top of the XR600/650 forum and look for Dave's Mods. It should have a .pdf file linked in there somewhere with illustrated instructions on how to go through the whole 650L carburetor, including changing the jets. There are also numerous threads about doing plug readings to dial-in the mixture.

 

 

My experience is the opposite. My bike will start to blubber and load up on the low end (pilot circuit) and become a lot tougher to restart as I go up in elevation, but it clears out a bit and runs better at ~50-100% throttle (main circuit). It picks up power across the board and cleans up a lot at low elevation, leading me to think that it isn't a case of lopsided (rich pilot/lean main) jetting. I doubt it's lean anywhere with 68/170 brass. Also, the more power an engine makes, the more sensitive it will be to air density changes because a small drop in density equates to a larger drop in power and that means a larger drop in fuel demand and, thus, jetting.

 

I've done the wire trick through a jet before, too. :D

well I was reading about desnorkling and uncorking. I have a foam filter but didnt desnorkle because I dont want to mess with stock jetting etc if I dont need to. Right now i'm at 800ft in NJ, so if i desnorkled could that let the necessary air into the motor to counter the altitude? Or am I way off 

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