FMF Pipe and jetting...

SterlingYZ · Mar 23, 2003

OK, I just finished rebuilding my top end and it runs great. However, I am running an FMF Fatty pipe w/Boyseen reeds and I am not sure what main jet to run. I understand that tweaking this to perfection takes testing, but is there a figure to start with, so I can buy 4 jets or so... I ride a YZ125J1 in the MD/DC/VA area (sea level) with temps right now hitting 70s, soon to be higher. Considering I am running a high performance pipe and reeds, how should I adjust my jetting so that my bike rubds safely, without overheating? Is there a rule of thumb to follow here? Thanks in advance for all of your help with this. This is the ONE area of MX knowledge (OK, OK BESIDES changing fork seals) that continues to elude me!

-MSW

"Keep your Wheels on the ground, and your feet on the pegs" Larry Maiers

96717 · Mar 23, 2003

what year is your bike??? 01?? i've used the Boyseen pro series reeds before i droped the main 1 size from stock. for now i would use the stock main until it does get warmer. i'll try helping you out

SterlingYZ · Mar 24, 2003

Thanks for the response, My bike is a '97 YZ 125, and the only mods on it are the FMF pipe and silencer, and Boyseen reeds, which need to be replaced at this point.

CamYZ125 · Mar 27, 2003

I was running a 350 stock (7,000 elevation) and stepped up to a 360 when I put an FMF Fatty on. Did a few different plug checks, and 360 seemed to be the closest for me. So I guess my advice would be, start at or around stock, do a couple plug checks, and continue fine tuning from there.

FMF Pipe and jetting...

SterlingYZ

96717

SterlingYZ

CamYZ125

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