How much will Altitude matter

[Bo0YaA]

Ok well I was going to wait on buying a 350x carb for my 250sx but I found one local for $30.00 and its as clean as they get.
Ive read many posts about the need to rejet the 350x carb to work well on the 250sx. My question is, I live at about 4500ft above sea level and I ride alot of times in the 7000 to 9000ft level. How will this affect my need to jet the 350x carb?

Also I am still looking or a pipe for my 250sx if anybody has one they want to part with please let me know.

[ccdhowell]

As the air gets thinner, rise in altitude, the bike will run richer and need a smaller main jet. If I was riding up and down allot of altitude variation, I'd consider one of these Dial-A-Jet things from Thunder Products. I've never known anyone that used it, but it looks good to me. Chris

[Rustytinhorn]

I live and operate at 5280+ feet above sea level.
I do a ton of trail riding on my little Atc200. When I lived in central Utah I would start out at about 5500ft and go to about 10100ft in a few miles, even though it still went higher. They had signs along the road marking every 1000ft you climbed it was that steep.
My 200 is jetted slightly rich at 5280. I can ride that high with no problem. There is a little less power due to the thin air, and I believe that it had a slightly harder time idling at 10100ft, because the higher you go the thinner the air.
However, the higher I went the colder the air became also, which makes it more dense.
What I would do is jett for the lowest elevation you will be riding at, and just leave it at that. That way you are safe. From my expereince, 4 strokes do well at changing altitudes without much problem.

2 strokes, on the other hand, seem to be tempermental. I usually stay within 3500 feet of 5280 with my two stroke, as I t doesn't see a lot of trails that my 200 does, so I guess I cant help you much there elevation-wise.
However, I do know that a 10 degree change in temperature will make or break a two strokes performance. at this elevation, I can jet all I want to for the hot day weather and never quite get the power I want, but as soon as night hits and it drops into the 60's my 250 will come alive. I have played and played with the jetting, but I think that it is simply due to the fact that my 250r just needs that amount of colder and denser air to really scream properly.

Hope this helped some as youi are kinda short on replys.

[Rustytinhorn]

In a nutshell-if you are going to ride at 4500ft at all, then jet it for that altitude, as you will always be able to ride at anything 4500ft+ with that jetting.
If you ride it for a while at the 7000ft elevation and it keeps fouling the plugs, then you might want to consider jetting it for the higher elevation, but then if you go back to ride at 4500 you will have to switch it back so you dont run lean and burn up your engine.

[Bo0YaA]

Hey Rustytinhorn,

What part of Utah you in? Most of my riding is done up Farmington Canyon just east of Lagoon if you arent sure where farmington is. So what I think I will do is just leave the stock 350x jets in it and if its burning rich I will throw the 250sx jets back in.

Thanks to those who replied

[Rustytinhorn]

I live up in Mantua, just east of Brigham, thats sweet I didn't even notice you where from UT. COOL.
Sorry, I don't have any experience with the 250sx or 350x, so I'm not sure how closely the carbs and jetts are, or would have to be played with in order to make the correct mixture. Maybe someone that has done this swap could chime in, I;m sure there is someone???

[Bo0YaA]

Ahh yes the Mantua Rainbow trout made famous by the late great Doug Miller!!! I know right where you are. Lots of good riding up in those parts for sure. Your right up there in the spot I drive bye and say "Damn I wished I knew somebody who lived in Mantua so I could get access to all that beautiful deer country" lol

[Rustytinhorn]

Theres tons of deer up here, but I'm not rightly sure where the public/private boundaries are as I'm not much of a hunter, although I have thought about it before. I like fishin though. If I wasn't so scared of the ice breakin through on the lake I would love to make a track for ice racin in the witner. I've driven on it before, but with all the springs makin all those slushy spots in the lake when its supposed to be frozen solid, it kinda takes the fun outta it. Gotta be carefrull.

[Bo0YaA]

Damn, i was hopin you were a hunter that had 100's of acres and were gonna invite me up for a hunt lol jk. Well I do have a little boat that would fit right nice on that little lake and if you ever do decide to get into huntin, let me know thats a passion of mine.

[Rustytinhorn]

Will do. gfjdfjfgjfkd (Needed to type my 10 characters to post)