03 wr250 jetting

[rooster]

start with 2 jets leaner and check response in the midrange-- ie: lower rpm range and roll on the throttle up a small hill, it should run through the midrange to the top end cleanly, then on top end ( in 4th or 5th gear ) it should run wide open for 10-20 seconds cleanly as well. :

[dirtyboy]

Hey troops,

I have been getting my 2003 wr250 ready for the season and have a question regarding jetting. I just bought an FMF factory 4 midpipe and muffler and want to re-jet my machine. It has the stock 172 main and I am wondering what size I should now go to. Anyone played with jetting on a similar setup? I'm thinking a few sizes down but would welcome suggestions. Thanks!

Rod

The Factory 4 is less restrictive than the stock silencer. It looks like you might have had the stock silencer on the bike by the look of the picture.

With a more open pipe, and an airbox that can keep up, I think that you would need to go with a richer main jet. Depends a bit on the needle but I'd start with a 175 or 178. I always use the YZ exhaust cam on my WR so it may be a bit different, but I used a 180 with the JD needle and I think a 178 with the stock needle.

If you tell me a bit more, I'll look in my log book for my '03 and tell you exactly what I was running 2 years ago. I had the YZ cam and the FMF PowerCore 4 muffler.

I've since turfed the PC4 due to noise in favor of an FMF Q. The Q is more restrictive so I had to go 2 sizes smaller on the MJ and 2 clip positions leaner on the needle changing only the muffler from the PC4 to the Q. Works good with these settings.

[WR_Dave]

Your bike was built for sea level so it came to you in a state of too rich , The new pipe will lean it down some but I'm betting that you could go to a 162 main, a 40 pilot jet and drop the needle one clip position then fine tune with the fuel screw. This set up works great for high altitude single track riding, you may want to stop at a 165 main jet if you ride alot of cutlines and fire roads. My .02--WR Dave

[rooster]

try the fatter jet- when you get the main jet proper then the bog should be pretty small but definite in one spot- then you should monkey with the needle settings-have you checked the fuel mixture screw? At hot idle you should be set approx 1.5- 3 turns and have no bog just off idle when you crack the throttle- if you have the fuel screw more than 3 or less than 1.5 turns then you should change the pilot.. You may want to invest in one of those aftermarket fuel adjust screws that makes adjustment possible with out carb removal- it takes time to get it right but it is worth it , please consider the noise level if you are going off-road

[BigD]

Like rooster said try adjusting the fuel screw. Off idle bogs may be fixed by adjusting fuel screw, pilot jet or even leak jet. With putting, the less restrictive pipe on your bike it is going to be running leaner so turn out the fuel if that does not help go to a larger pilot jet. One of the best mods I did to my bike was make an adjustable fuel screw. All I did was use some automotive brake line drill it out a bit and locktight it to the fuel screw and put a roller pin in the other end to turn it works awesome and saved me 50-60 bucks. If you check out this web site under tech articles and "adjust on the fly” fuel screw that is were I got the idea from.

http://motoman393.thumpertalk.com/