Do I have to rejet 2017 yz125 with fmf fatty and Powercore 2.

Michaelh1001
I bought a 17’ yz125 with a fmf gold series fatty and powercore 2, I’ve never touched any of the jetting but would like to know if it could possibly run better if I had the proper jetting. I’m aware of the JD jetting kits but I’d like to know what kind of jets+needles I would need. Thanks
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sandhills
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sandhills 8/11/2022 8:20am
8/11/2022 8:20am Edited Date/Time 8/11/2022 8:24am
Pretty much every yz125 could always use some jetting work. It's never as simple as this pipe + this silencer = these jetting changes.

Ride it around and try all throttle and RPM combinations, whack it open at different RPMs, roll it on too, hold it it a quarter or third or three quarters, if you can't find any bogs or sputters then it's already pretty close.

If you find it's not delivering smooth and strong response anywhere I would start with some OEM jets: Main 400, 410, 420, and 430, pilot 35, 37.5, and 40, needle is probably ok but I would buy an extra OEM clip if I'm ordering stuff. Look in the OEM parts section of whatever your favorite source is, I use rocky mountain. Don't get aftermarket jets, pro-x etc.

You can use Pro Circuit as a starting point, but theirs are developed in socal at sea level and are usually too rich for anywhere else.

https://www.procircuit.com/jettingspecs11.htm
Michaelh1001 8/11/2022 12:35pm
8/11/2022 12:35pm
sandhills wrote:
Pretty much every yz125 could always use some jetting work. It's never as simple as this pipe + this silencer = these jetting changes. Ride it...
Pretty much every yz125 could always use some jetting work. It's never as simple as this pipe + this silencer = these jetting changes.

Ride it around and try all throttle and RPM combinations, whack it open at different RPMs, roll it on too, hold it it a quarter or third or three quarters, if you can't find any bogs or sputters then it's already pretty close.

If you find it's not delivering smooth and strong response anywhere I would start with some OEM jets: Main 400, 410, 420, and 430, pilot 35, 37.5, and 40, needle is probably ok but I would buy an extra OEM clip if I'm ordering stuff. Look in the OEM parts section of whatever your favorite source is, I use rocky mountain. Don't get aftermarket jets, pro-x etc.

You can use Pro Circuit as a starting point, but theirs are developed in socal at sea level and are usually too rich for anywhere else.

https://www.procircuit.com/jettingspecs11.htm
Honestly it runs great, it pretty much never bogs and sounds like it’s alive at all times. I’ll just leave it as it is
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