rejetting after new pipe

im getting a pro circuit pipe n header n i wonder if i need to rejet. i dont know what is my current setting in the carb. at the momemt , but what in general i should do?

This is what's in my YZ-timed 01' WR426. Bike feels electric...

Main Jet #168- 4MX-14943-91-00

Pilot Jet #48- 4MX-14948-06-00

Pilot Air Jet #100- 7A9-14943-27-00

EBLN Needle (yz250f)- 5NL-14916-EN-00

hey its all depends on the weather and the humidity, and the temp outside

damn thing poseted before i was done. i am in az and right now its been about 70-80 degrees - oi run the FMF stuff and I am running a 168 main, 42 pilot witch is stock, needle in the 3rd and fuel screw 2 turns out

Gal :) Go with rat & Jamracer, Have you recieved the Pipe ? What Model ? Does ProC suggest any jetting ?. I run a r4 from Wrigt Bro, the bike ran fine with the stock jets 42 Pilot, 162 main and the needle in the stock setting 4 up from the bottom. I ended up with a

45 pilot

168 main

Needle 1 down bringing the needle up (Richer)

Agree with Rat, That jetting has a lot to do with many conditions, Air Temp, Humidity, Altitude and so on. I will change my pilot back and forth along with the needle up or down dependin how the day is.

Serious search the threads for jetting you can write a book

Good luck

more info.

i got the bike from a friend who told me the jetting in the carb was stock, he bought the bike in new york. the bike is with stock everything but the 10oz flywheel weight.

the bike is running great now and i live in israel - sea level,5-40 c (winter to summer) and the humidity is around 35-80 % (winter to summer).

jamracer is getting me the pipe from florida its a pro circuit for motocross with no restrictions and as he said its one version before the t4.

Hey guys,

It's the 304 series motocross pipe (with oversize header) that will be going on the bike. The jetting specs would be the same specs as Florida, as far as summer is concerned. For winter, he'll have to tweak it a little. Also, the pilot that I mentioned would be in conjunction with the BK Mod.


Got to Motomans site he has a real good yz jetting spreed sheet that can help

Look under

YZ426 jetting tuning spreadsheet

its an excel sprd sht , it has good numbers to start with for elevation, sea level and all

MotoMan is to good to us :)

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