Author Topic: 6000 ft elevation change? (Read 4055 times)

JesseA420 · « **on:** January 26, 2014, 07:50:59 PM »

just bought a bike with a 350 esr cylinder, +4 crank esr 11 pipe, and a 39mm pwk that is jetted for 7000 ft elevation. I ride at 1000 ft. How should I rejet accordingly? Several sizes bigger main and pilot to begin, or just 1 each or more. Just trying to get a baseline. Any help?

JesseA420 · « **Reply #1 on:** January 30, 2014, 09:02:24 AM »

thanks for all the help guys!

rsss396 · « **Reply #2 on:** January 30, 2014, 09:16:14 AM »

sarcasm? try helping yourself to the technical section for answers

http://trx250r.org/showthread.php?1400-KTM-temperature-and-elevation-corection-chart

JesseA420 · « **Reply #3 on:** January 30, 2014, 09:52:33 AM »

"Problem with fuel, intake, or other carb related issues? Post it here." was looking for a generalization to baseline from, seemed like this was the correct place to post, no? the description of this section seems to lead to that assumption.

i dont know all the whos who and whats what with the back and forth of the two R sites, but i got 2 pages of helpful responses over there.

rsss396 · « **Reply #4 on:** January 30, 2014, 10:09:17 AM »

You posted in the correct area, and for what ever reason you did not get a response. But what we do have is allot of information to help you make a educated decisions that can be found very easily if you look.
You have a base line now at 7000 ft so if you look at various charts you can make a change that will be predictable, maybe not exact but close. from there you make your fine tuning adjustment or jet changes.
To many people do not know how to tune a carburetor simply because they have never spent the time to try and learn how they just want to know the answer.

the old saying : "Give a man a fish, and you feed him for a day; show him how to catch fish, and you feed him for a lifetime" holds so true

JesseA420 · « **Reply #5 on:** January 30, 2014, 10:29:18 AM »

when i initially looked for information, i did not find this thread you posted. now that i look closer, i see where it is. the small technical section is at the almost very bottom, and when you skim through and see the main section of carb exhaust cylinder chassis "workshop" sections, it leads to posting questions rather than it being known that the majority of information most people need is simply at the very bottom of the main page in a small section.
just a new guys point of view, but it would probably be helpful to people just looking for information if the technical section was towards the top of the main page where it would be more easily found.

rsss396 · « **Reply #6 on:** January 30, 2014, 10:37:10 AM »

I agree it can be missed easily, and by the way welcome to our site you and dont let this one instance tarnish the view of our home.
Sometimes good questions never get seen by the right people that may have good input to share, it just happens for various reasons and sometimes you have to bump it back to the top to get a responce.

rk88r · « **Reply #7 on:** January 31, 2014, 03:23:26 PM »

Quote from: JesseA420;24044

"Problem with fuel, intake, or other carb related issues? Post it here." was looking for a generalization to baseline from, seemed like this was the correct place to post, no? the description of this section seems to lead to that assumption.

i dont know all the whos who and whats what with the back and forth of the two R sites, but i got 2 pages of helpful responses over there.
http://www.trx250r.net/forum/intake-fuel/26599-6000-ft-elevation-change.html

I saw your post over there first and responded there. I would always check here first, a lot of info never makes it out of the chat room though.

Jerry Hall · « **Reply #8 on:** January 31, 2014, 06:14:16 PM »

Atmospheric conditions, temperature, humidity and altitude (barometric pressure) affect air density. None of these 3 variables are linear but humidity is the least linear in the range of conditions where humans can exist. If you follow these rules of thumb you will be close on your jetting as long as you have an accurate baseline to work from.

Air density changes about 3% for every 1000 feet of elevation when the temperature and humidity does not change. Air density changes about 3% for every 15 to 20 deg. F . The effects of humidity is a little more complex because of it its non linearity in the range of temperatures present where we ride.

If you have a Mikuni carb., Mikuni's jets have a FLOW number stamped on them.

Example:

Going from a 300 to a 310 main jet is a 3.2% change in fuel flow at wide open throttle.

Going from a 450 to a 460 main jet is a 2.2% change in fuel flow at wide open throttle.

If you are using A Keihin carb. you will have to do a little math and calculate the AREA of the hole in the jet. Keihin jets have a coded jet diameter stamped on them. If the jet says it is a 170, this means the the hole in the jet should be 1.70mm. A 175 main jet has a 1.75mm hole and so on....

Example:

A 170 main jet should have an area of 2.269 mm^2
A 175 main jet should have an area of 2.405 mm^2

the ratio of areas is: 2.269 / 2.405 = .943

To find the % change in going from a 170 to a 175 jet use the following formula:

(I - ratio of areas ) X 100 = % difference in flow rate between two different jet sizes

(1 - 0.943) x 100 = 5.7 %

You should now have enough information to figure out how many main jets you should need to richen your main jet from your baseline setting.

jcs003 · « **Reply #9 on:** January 31, 2014, 07:12:18 PM »

was this bought from someone in sante fe, new mexico?

john