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JD Jetting HELP

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I purchased the JD kit for my '04 250f and it didn't come with any instructions or recommendation for where to start and what needle to run. I am in UT and ride from 4000'-6500' and 40*-100*. current temps are 80* in the mornings and 95* afternoons give or take 2-3*.

I'm hoping somebody still has their instructions that can advise a good starting off point.



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My JD instructions for an 04 WR250F say (your model year may be different, better to call JD):

Cold temps/low humidity

0-3000' elevation: 185mj Blue #5 needle

3000'-6000': 180 mj Blue #4

6000'-9000' 175 mj Red #3

9000'+: 170 mj and Red #2

High Temps and or high humidity change the mj and needle jet lower.

Blue is used for cold temps but not at your elevation. Red needle is leaner in the bottom end.

Here is also a great thread that should give you some guidelines if you were to NOT use the JD kit.

Thread link: https://thumpertalk.com/forum/showthread.php?t=790816&highlight=

In an effort to add to the already deep knowledge base here on TT I thought I would document my build up of my 08 WR250F from "as I purchased it" and on.

When Im done it will have: Athena 290, STG1 HotCams, FMF power bomb head pipe and Q4 muffler.

So here goes. The free mods were already done by the PO- supposedly dialed in and running great (snorkel out, GYTR muffler insert, grey wire and rejet). An hour with the bike at the practice area and it was obvious this was not the case. Blubbery throttle, bog, no low end, but pulled like a 2 stroke on top.

First things first- jetting. Starting with the main, if you don't have the main right, don't waste time with any other settings. At this point I should mention I am in Colorado Springs, CO- 6215 ft above sea level- so this should make for some good reading for those of you who travel to high elevation to ride. Bike on the dyno, air fuel meter set up, ready to test:



The following dyno shows the as delivered and where I stopped. As delivered 165 MJ was giving A/F ratios in the 10's, way too rich to make peak power. Leaning it out would net an increase in hp. All the way down to a 140 before the point of diminishing returns was found- back to a 145 to get the A/F to the mid 12's:


The peak numbers seem very similar- with only 1hp gain, but look at the area under the curve, more hp and tq sooner and with longer duration.

Next: dial in the idle to 3/4 throttle settings, stay tuned!

Edited by alligatorman
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