Jetting

[RideRed193]

I realize that there's not as many people on the boards as there used to be, but maybe someone here will see this and be able to offer me some advice:

I have a 2003 KX250 and just moved out west from Michigan. The bike is stock, except for a Pro Circuit pipe. My question is about jetting. I was riding at probably 800 or so feet above sea level in Michigan. Now in Montana, I'll be riding at around 5200 feet mostly and sometimes 7000-8500 feet.

I would imagine that I will need to re-jet to ride in the higher altitudes, but I have no idea how to go about this. If anybody has any advice on this, that would be awesome.

These are the jets that the bike has in it right now:

Main- 162
Pilot- 52

Everything else is stock (needle, slide, etc.)


Thanks.

[Sheriff]

In high altitude, oxygen is rare compared to sea level. I believe you'd have to go leaner. The best thing I could suggest is to start riding, get the bike to operating temperature and see how it behaves, then make adjustments.

[Falcon991]

You will definitely need to go leaner. That means a smaller mainjet and move the clip up on the needle (so the needle sits lower in the throttle slide.) Go in small steps with the main - I's start out two sizes smaller and go from there. Ride for a short period of time and look at the spark plug. If it's black and oily, you should go leaner. If you ever get it too lean, it will look white. Tan is the color you are looking for, Good luck!

[copsey]

Rule of thumb is one jet size per 1000 feet if I recall correctly.

Leaner for higher and richer for lower.

But like Falcon said you'll have to play with it to get it spot on.

[electro211]

The easiest way to jet a bike is to purchase a JD jetting jet kit. They are pretty pricey, but they give you all the jets you need, and a altitude chart. The instructions are clear. It tells you what jets to use at the altitude you are at, and the temperature you are at. I don't know if they make kits for 2 strokes, but the one in my 4 stroke works great.

[Falcon991]

The easiest way to jet a bike is to purchase a JD jetting jet kit. They are pretty pricey, but they give you all the jets you need, and a altitude chart. The instructions are clear. It tells you what jets to use at the altitude you are at, and the temperature you are at. I don't know if they make kits for 2 strokes, but the one in my 4 stroke works great.

Are these specific to each make/model??? That would be pretty amazing. If so, no wonder they're pricey. I know from my old 125 days that even each of those bikes needed different jetting (my '00 YZ125 was different from my '01, etc...) Do they go out and test each new bike at different altitudes & such?

[electro211]

Are these specific to each make/model??? That would be pretty amazing. If so, no wonder they're pricey. I know from my old 125 days that even each of those bikes needed different jetting (my '00 YZ125 was different from my '01, etc...) Do they go out and test each new bike at different altitudes & such?

They are specific to each bike. I don't know how they test each model, but I have never heard any complain about them. They know there stuff, and will also answer any question you have. Its a great company. And, no I don't work for them, or recieve any discounts, just a great company. :thumbsup: