FMF pipe on 2001 YZF

Hi Guys, another newbie here...

I have a 2001 yz250f and have just added an FMF Powercore IV pipe. The bike runs great but I think is running a little lean. It really seems to run out of steam at high rpms. Is this something that can be adjusted with the fuel screw or do I need to be changing jetting?



Hey dude, welcome to TT. The fuel screw adjusts the pilot circuit only(low end response). For the top end, you need to rejet the main, stock I believe is 178, so you are looking at a 180.

On some pipes you might need to change the pilot usually up one. Stock was 40 on that bike I believe. Good luck.

After opening up my WR I was on a familiar firebreak tapped out in 5th and found myself looking for another gear. what I needed was a larger main jet boy, what a difference!

You might have to tweak the jetting (main, or raise the needle one clip positition) Cold weather makes a difference too.

FMF should have jetting reccomendations on their site to give you a starting point.

I'll swap the main to a 180 and give it a try. Thanks guys!



I had the same system (with header and Power Now) and went one up on the main, raised the needle on clip (richer) and uped one pilot jet for easier starting. Overall, I needed to richen all up for cleaner operation. Once jetted, the bike performed way better than stock. Downside was noise level was higher than stock which was a bit of an issue as I ride woods. I fixed that by custom making a tube with a variable baffle inside it. I fixed this to the pipe via drilling and bolting. Result was less noise and perhaps a bit of a power loss on top (hard to tell as less noise gives the impression of less power) but it satisfied the noise requirement. There are now professionally built quiet cores and end caps if you need to get one.

Good Luck :)

Thanks Kantoniak. I had wondered if I should adjust the needle after changing the main. Do you notice any problems when the weather changes? I rode last weekend in a balmy 60 degrees and it seemed to run better. Started better, too. Did changing the PJ make much of a difference in starting?



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