Need Help!!! How to jet a 1986 250r ATC???

[THE PETE-STA]

Hey fellas, I just bought a pair of 1986 250r's out of Utah, well the elevation is way higher out there and the seller told me I'de have to have them jetted for the elevation out her, Well I've never done this before, but I hear it's not that hard to do, I'm pretty mechanically inclined, But don't know how to do it. I wanna learn how to do this myself, could you guys shed some light on how to do this or is there a website somewhere where it shows/tells you the steps? I would greatly appreciate any help guys.

Thanks, Pete

[ceaserthethird]

Post some pictures, will need to find out what carbs are on them and what else is aftermarket...

[200XMichigan]

Here's some jetting info:

Altitude Compensation

For our first example let's say we find a new riding area WAY up in the mountains. Our jetting is dialed in for our usual riding area which ranges from sea level to 1500 feet. Our NEW riding area starts at 4000 feet and goes up from there. Going to a higher elevation will require will require a jetting change but which way? Like our fuel density, air density can also change. Higher elevations have less air density then lower ones. At high elevations our engines are getting less air, so they need less fuel to maintain the proper air/fuel ratio. Generally you would go down one main jet size for every 1750 to 2000 feet of elevation you go up (info for Mikuni carbs). If you normally run a 160 main jet at sea level you would drop down to a 140 at 4000 feet. Something else goes down as you go up in elevation is horsepower. You can figure on losing about 3% or your power for every 1000 feet you go up. At 4000 feet your power will be down about 12%-even though you rejetted! For our second example let's say we are still at our new 4000-feet elevation riding area and a storm comes in. We head back to camp and ride it out overnight. The next day there's a foot of snow on the ground the skies are clear and it's COLD! Aside from getting the campfire going and making some coffee you should be thinking about jetting again! Cold air is dense air and dense air requires bigger jets. If the 140 jet ran good the day before you will need a bigger jet to run properly today. If the temperature is 50 degrees colder than it was the day before you can actually go back to your sea level jetting, a 160 main jet! If you don't rejet you can kiss your assets goodbye when you rebuild the seized engine. Air temperature makes that much difference!

You went from higher elevation to lower elevation and your machine will be operating lean for its altitude. Ball park guess from where you got it to where you are you will need to go up 3 sizes to get close. I wouldn't run it at all like it is.

[atc007]

If they're the ones in your avatar,,I'm guessing he already had them right on the edge! And they're ported,piped,intake,and carbed. Drop down 4 or 5 sizes,ride them a couple miles,and you ultimately want to end up with your plug dark brown to light black. Any leaner,brown,grey,white,is bad news unless you're on top of it every run.

[200XMichigan]

He went down in elevation, he needs to go up in jet size. Dropping down 4-5 sizes from an already lean setting will kill it.

[willreed03]

Look in your manual, it will tell you how many sizes to go up depending on elevation changes.

[atc007]

He went down in elevation, he needs to go up in jet size. Dropping down 4-5 sizes from an already lean setting will kill it.

Yes,I know,,I MEANT to say fatten up 4 or 5 and drop down till your plugs reading right! Good thing he didn't run right out and buy jets!