Called a shop for some info....is this true?

[inv3ctiv3]

So I was always under the impression that if you were going to be going way up or down in elevation you had to re-jet....Well I ride in about 2,000ft of elevation and am taking my 400 to Mammoth which is about 8,000ft so I called a shop up there to ask how much it'd cost to have them re-jet and they told me there is no reason at all to re-jet....They knew where I lived and what the elevation was, they said it won't make much of a difference at all. What do you guys say?

[CJM]

Right.. Dont ever call that shop for anything again cause they are idiots.

Higher you go leaner the air is. If you left it the way it was at your elevation you would lose performance because the engine will be WAY to rich.

Would it harm anything, nope-just make the quad run like poop.

Explained here:
http://www.4strokes.com/tech/howtojet.asp#Altitude%20Compensation

Jetting compensation chart: http://www.ultralightnews.ca/rotax503/rotax2strokepdf/mainjetcorrectionchart.pdf

Personally id run 1-2 sizes bigger than you think you will need according to the chart.

[inv3ctiv3]

They said exactly what you said about running 1 or 2 larger but what they said is the temperature difference between SB and Mammoth this time of year actually compensates for the elevation, any truth to that?

[CJM]

Originally posted by inv3ctiv3
They said exactly what you said about running 1 or 2 larger but what they said is the temperature difference between SB and Mammoth this time of year actually compensates for the elevation, any truth to that?

Not sure about temperatures having that drastic an effect.

Its not gonna blow up thats for sure b/c its going to run rich and bog and not be lean.

[brokenmike]

That's weird cause iam in New Jersey (basicly sea level) and when I go to Pa My quads end up running lean and have to re jet richer.

[inv3ctiv3]

They did say it would run a little worse but they also said there is no reason to re-jet. The thing that's weird is I said I was gonna have them re-jet them (chance to make money for them) and they still said no reason to re-jet.

[Thumpin440ex]

If the air is thinner and the temp is that much colder, it might not make a big difference, but still will not be the same as you ride now.. The colder the air the more dense it is, inturn more oxygen in said amount of molecules.. This is only to a extant. Once you get so high up, there is hardly any molecules in there air.. PSI on earth is 14.7 @ 8k above sea level it will be a bit less.. So take that for what its worth..

John

[DnB_racing]

Originally posted by inv3ctiv3
They said exactly what you said about running 1 or 2 larger but what they said is the temperature difference between SB and Mammoth this time of year actually compensates for the elevation, any truth to that? temp definitely has some affect on jetting, and the advice the shop gave you is terrible....you will definitely want to go down a couple sizes in your main,, what size is in there now? and what temp is mammoth at this time of year?

cjm said go a couple sizes larger then the chart not 1 or 2 larger then you have... you need to go down or you will be rich, and loose power and possibly foul plugs leaving you stranded in the mountains

[CJM]

Originally posted by brokenmike
That's weird cause iam in New Jersey (basicly sea level) and when I go to Pa My quads end up running lean and have to re jet richer.

Quite odd, if anything you should be going down. But the fuel they sell there might have something to do with it or the area you ride in PA.

Im real close to seal level and using the chart I linked I should drop from 170 to 165 if you go up to 1640ft (where I plan on going to in PA). Honestly I think Ill just leave it and run rich.

[beags86]

Jetting compensation chart: http://www.ultralightnews.ca/rotax503/rotax2strokepdf/mainjetcorrectionchart.pdf

that f**king chart is no good what-so-ever, thats what i used to get my jetting right, and i am still chasing down problems at high elevs.

a good rule of thumb for jetting is to figure out your jetting and go one jet size higher then you figure. that way your not to lean.

jetting goes down as you go up.

yes you will need to re-jet for 8,000 feet.
another rule of thumb is to take your jetting at sea level and take 92-95% of that for your jet size.

then you need to buy 3-4 jets and play with it once you get to where your going to ride.
every machine will be different and you need to play with your machine to find the right setting.

[DnB_racing]

Originally posted by beags86
Jetting compensation chart: http://www.ultralightnews.ca/rotax503/rotax2strokepdf/mainjetcorrectionchart.pdf

that f**king chart is no good what-so-ever, thats what i used to get my jetting right, and i am still chasing down problems at high elevs.

a good rule of thumb for jetting is to figure out your jetting and go one jet size higher then you figure. that way your not to lean.

jetting goes down as you go up.

yes you will need to re-jet for 8,000 feet.
another rule of thumb is to take your jetting at sea level and take 92-95% of that for your jet size.

then you need to buy 3-4 jets and play with it once you get to where your going to ride.
every machine will be different and you need to play with your machine to find the right setting. the chart is a very good staring point, no it wont tell if your needle is all wrong or if your pilot circuit is way off, but if you really have it jetted properly for your elevation, then all that's really needed is a couple sizes down in the main just as the chart shows..

if your having issues then i would guess your problem is more then just your main, and its just showing up at the higher elevations,, the chart is only good if your jetting is were it needs to be from the start at your current elevation...

if you have to make major adjustment more then just the main when going up in elevation, then your other carb circuits are off


why do you say the chart is wrong? it shows to use at 8000 feet around 90-97% depending on temp just as you already mentioned.. whats wrong with that?

yes every machine is different but its still the same machine as your jetting at a lower elevation,, its still the same machine and pressure is still going to affect the machine the same when using the chart it is assuming the quad being jetted is already jetted properly

[CJM]

Funny, if I follow that chart and do it 170*.97 is about dang close to what your saying beags. Maybe im just lucky.

[inv3ctiv3]

I'll order some new jets this week, I gotta figure out what's in the bike now, I assume it's stock because the engine is completely stock and the bike was 100% original when I got it....Any good DIY's for changing the jets? I've done it before on my 3-wheelers but never my 400.

[CJM]

Just cause Im the best lol..

My jetting thread: http://www.exriders.com/vbb/showthread.php?threadid=463320

Its for a 450r carb but its all the same as the EX carb pretty much

[inv3ctiv3]

Alright it's exactly what I thought, I'm a good mechanic but I like to have as much info as I can before doing something on a new bike. I'll probably have to re-jet all my friends bikes too....thanks for the info!

[CJM]

Yep, yep.

Fyi you can just remove the drain screw on the carb and get a 6mm socket and a 1/4 drive ratchet and extension and change it out if your carefull threading the new one on.

[inv3ctiv3]

That's the plan, although I may need to adjust my pilot too right? I have rebuilt plenty of engines but I don't mess with carbs much cause I never have to so this is my weak point for sure.

[CJM]

Cant really "adjust" a pilot jet. You change them. What your probably thinking of is the air/fuel screw which is a fine tune adjustment for the pilot jet.

[inv3ctiv3]

Very true, I need to go order my new main jets tonight.

[beags86]

Originally posted by DnB_racing
[B]
why do you say the chart is wrong? it shows to use at 8000 feet around 90-97% depending on temp just as you already mentioned.. whats wrong with that?
B]

it's too rich, in the real world 97% is to much, you need to be close to the low end for it to be right.

and no this comment is not just coming from me, but all my fellow high elevation riding buddys are telling me this , and i am finding this out to be more real world then what the chart says..

but i agree the chart is a good starting point, and would definitely get you by for a trip or a few rides at some elevation. but for someone that rides every weekend at 8,000 and above it simply isn't close enough.

i found that the jet r us chart to be a little better. in my opinon.

http://www.jetsrus.com/FAQs/FAQ_rejet_elevation_and_temperature.htm

[DnB_racing]

Originally posted by beags86
it's too rich, in the real world 97% is to much, you need to be close to the low end for it to be right.

and no this comment is not just coming from me, but all my fellow high elevation riding buddys are telling me this , and i am finding this out to be more real world then what the chart says..

but i agree the chart is a good starting point, and would definitely get you by for a trip or a few rides at some elevation. but for someone that rides every weekend at 8,000 and above it simply isn't close enough.

i found that the jet r us chart to be a little better. in my opinon.

http://www.jetsrus.com/FAQs/FAQ_rejet_elevation_and_temperature.htm what are the three different numbers on the left of the chart for?one is for mikuni are the others for keihin or dynojet? its kinda vague on which carbs its for,

but i tried putting my jet numbers in both charts and used the same elevation change and temp change and they were both real close.....

but to be honest everytime Ive gone up to mountains Ive only had to drop a couple sizes in the main I never used a chart i just used the old fashioned method of listen, look, and feel ,,

never had any problem jetting for different elevations,
as long as my base line to start was good ,i never had to change pilot or a/f screw

just at the most 3 sizes in the main and that was the biggest change Ive ever had to make.. but it was for my sled in the winter in the white mountains... as long as you have a full understanding of what to adjust and why, it should only take a few tries and have it right

[inv3ctiv3]

Went to my local shop and looked up the factory recommended settings for the elevation. It recommends a main of 142 for 3k-8k in elevation. I bought a 142 and a 140, I think I'll be covered with those, I might get a 144 just to be safe.