jetting my kx 250 for a fmf pipe

[redfabkustomz]

hello
i was wandering if any one knew how close the the jetting will be from stock. if i put a fmf gnarly pipe on my 99 kx 250?
it was a 150 main when i got the bike and i jetted it with a 152 main for sea level.
my altitude is about 1500 feet that i do most of my riding. but i will be going to the coast this summer?
has any one put an fmf pipe on there bikes and if so? what was the jetting like?
thanks red

[KKXR400R]

I would just throw the pipe on and see how it runs. I know of a instances where have had to lean out their bikes after installing their pipes. After you get the pipe installed, take a mental note on how the bike ran and compare it to the ride prior to that. If it runs lousy jet start getting your jets out and work out the kinks. Good Luck

-Kevin-

[The Baron]

FMF should have jetting specs on their website. Check that out. If not, ProCircuit does for sure. I believe all of their specs are for sea level.

[LoKi]

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[The Baron]

There you go!

I tried to link but my dumb work PC is blocked from that site. Stupid IT dept.

[ossagp1]

My take on aftermarket pipes are that if you don't need to rejet to get the max or ulimate out of them, then you were jetted wrong for the stock pipe. Truthfully, sometimes you can get a noticeable amount of increase from just adding an aftermarket pipe. (You pick the brand.) Paricularly when the noisy, less restrictive silencer is added with it. It is a combination of that decrease in restriction and what was likely a too rich across the board jetting to begin with from what I find.

The Gnarly, though is a good replacement. I got one second hand and I like the way it has held up. Stock pipes are way overpriced new, so it is a good replacement pipe for sure.

[The Baron]

I totally agree with Ossa. Lots of people run rich simply because they either are afraid of seizing due to a lean condition or they just don't want to take the time to dial in the jetting. Taking the time to properly jet a bike can take it from good to great with no more than a little bit of time and a few dollars for jets.

The only problem with tuning it so precisely is that it will then be even more finicky in regards to climate changes. Most folks run good enough jetting just so they don't have to mess with it much. I would rejet at the track all the time but as I've gotten older I have decided that good enough jetting is good enough for me.

But yes, a good exhaust setup can make a world of difference in the performance of the bike, especially when jetted well.

[ossagp1]

That's OK "B", most of us run "chicken" jetting. I had to learn it with my first KX500. (It came from the factory with some airleaks which were big enough that I was tempted to just mount carburetors on them.)

[The Baron]

Originally Posted by ossagp1

That's OK "B", most of us run "chicken" jetting. I had to learn it with my first KX500. (It came from the factory with some airleaks which were big enough that I was tempted to just mount carburetors on them.)

That's funny!

I got a kit from James Dean for my RM125 about a week ago and am in the process of getting it dialed in. It's sort of a hassle starting over from scratch. His needles are so much fatter than stock that they require a much larger main jet so I'm basically back to square one. It's sort of a pain. He recommended a 420 main, up from my 370 with the stock needle, and that was too lean. Needless to say I'm not too excited about going through this again but I'm even less excited about going through my 06 YZ450. That thing is the biggest pain in the butt.

[redfabkustomz]

thanks for the info! my pipe didnt show up to day but for sure tomarrow he said?? haha we will see! ill let you know what happens tomarrow!
red

[redfabkustomz]

well i think that i got it figured out! i went up 10 on the main! to a 160 and from a 45 to a 48 on the pilot seams to run good and it smoke good out the pipe. going to take my plug to the shop and ask if its looks ok!!!
some one said that i mite need to move the setting on the needle??? how will i know if it need it? and what will that do??
thanks red

[ossagp1]

The needle basically has the most control over carburetion at 1/4 to 3/4's give or take a little. If you are getting pinging in that range of throttle opening, you need to lower the clip on the needle (toward the pointed end). This is called raising the needle (because that is what it does) and allows for more fuel to make it's way into the intake tract at those throttle settings. Raising the clip up lowers the needle, and if you study the taper and the straight part of the needle you will see why the control really doesnt start until the straight part has cleared the needle jet passage and how the taper allows more fuel as the throttle slide and needle are raised.

The best way to find out if yours needs changing is to ride it, think hard about how it works at responding at midrange )1/4 to 3/4) throttle and then changing the needle up and down to see if you like the change, or liked it the way it was. Take notes, at some altitudes or temps you may like it one way or the other. But if it is pinging when you roll the throttle open, raise the needle (lower the clip) and see if it goes away.

A plug reading probably won't tell you much about your midrange, it is usually used to tell how the engine jetting is at full throttle. The needle will affect full throttle in many cases too (depending on the needle itself sometimes) but that is not it's primary function or primary range of adjustment.

[redfabkustomz]

thanks for the info
i had took the carb apart friday and move the clip down to the 5th setting. went for a ride and if started fouling out the plug. and also missed a bit as the pipe came on! i move the needle back to the 4th setting and it seams to run pretty good i think ill leave it for now
i also took the plug out sat. and it did look a bit rich. i cleaned my air filter. it has two fillters on it! one stock and one for the sand! ill leave the outer one off and go for a ride soon!