2000-02 YZ426F User Jetting Database

Model: 2002 YZ426f

Timing: YZ

Main Jet: 165

Pilot Jet:42

Starter Jet: stock?

Leak: #58 installed (MOD)

Fuel screw: 1/2 -3/4 turns out

Needle:Yamaha NDJQ at #4 clip (1 needle leaner than stock "P")

Air box: no lid, K&N ( I hate cleaning the foam filters)

Pipe/muffler: DRD 3.5 X 14 w pipe & quiet core insert

Altitude: 1300 feet

Temp:current 80-100F

Humidity: 70%

Other: BK mod sub 1 second squirt, #58 leak jet, Boysen AP cover

Degree of satisfaction; Runs well. I worked a long time to beat a bog and have it reduced. The bike gives conflicting signals (ex. Fuel screw in all the way increases RPM but runs better under load with this pilot). If I go up on the pilot/fuel screw =slight rich bog on the AP, if I go down= slight flat spot in the middle of the RPM range but good snap higher and lower. The 42 pilot gives the best loaded performance. Tunable BK mod bolt helps a lot. I like the leak jet as well. I can tune across more tempreture range.

Model: 2001 YZ426f

Timing: YZ

Main Jet: 160

Pilot Jet:42

Starter Jet: stock


Fuel screw: Stock

Needle: stock at #3

Air box: no lid

Pipe/muffler: White Bros E-Series

Altitude:1200 feet and less

Temp:current 85-110 F

Humidity: >20%

Went to Flagstaff/Stoneman Lake area and changed to:

Timing: YZ

Main Jet: 145

Pilot Jet:40

Starter Jet: stock


Fuel screw: stock

Needle: stock at #3

Air box: no lid

Pipe/muffler: White Bro E-Series

Altitude: 6200 feet and up

Temp:current 84-95 F

Humidity: >10%

I still noticed some rough running with these setting, but if you were on the gas, it was fine. I should have probably put a 38 or less PJ in it, but didnt...

Model: 2000 YZ426

Timing : YZ

Main jet: 165

Pilot jet: 42 I think

Fuel screw: stock ?

Needle: OBEKQ

Airbox: U/modified w/Twin air filter

Pipe/muffler: Stock

Alltitude 0-1000ft

Temp: Depend time of year -5'C to 45'C degrees

Humidity: Depend time of year 25% to 75%

Other: Want softer, smoother power, put a OBEJP needle in @ 3-4 clip and disonnect the TPS. :p

Want some aggression throw the OBEKQ in. 4th clip, yee-haa !!! :ride::p

DO- I need to do the BK mod. These both show that flat spot, more so with the OBEJP needle in place...... :applause:

Model: 2001 YZ426F

Timing: 03 450 autodecomp cam

Main Jet: JD Jetting 170

Pilot Jet: stock

Starter Jet: stock

Leak: stock

Fuel screw: Stealth Racing with spring kit - 1.5 turns out

Needle: JD Jetting #4 clip blue needle

Air box: No lid with oiled foam filter

Pipe/muffler: stock

Altitude: 700ft - The flat lands of Illinois

Temp: current 80-90F


Accelerator Pump: Stealth Racing

The bike is starting so easily and is great at low speed without stalling. No bog or hesitation that I've noticed at this point.

I have 2000 YZ426 with an 03 YZ450 carb

50 pilot

165 main

factory R & D ep cover stk. diaphram

fuel screw at 1.5 turns out

DEP headpipe with a Doma muffler

YZ450 exhaust cam mod

currently running B33 gas, but the same condition exists with pump gas

bike misses under a low/no-load on the motor

this is in different throttle positions and not just one spot

but under a load it never misses a beat,and when you chop the throttle there are no afterfire pops at all

TPS is hooked up at the moment

@ 1200 ft elevation here in DFW

tailpipe is chaulkwhite in color after a ride

Any ideas?????



READ BEFORE POSTING!: This thread is intended to be used as a reference collection of jetting used by members ONLY. Please use the provided template below, and post only the jetting you currently use, along with any pertinent comments. Post only in the correct thread for your model bike.

DO NOT ask questions or discuss the information posted here in this forum. If you want to talk about anything here, please do so in a new or current thread on the topic and use a link to the particular post you wish to discuss. Posts not complying with this format will be removed without comment.

NOTICE:The people who post here are of all skill levels. This information is only intended to let you see what others are using, and cannot be taken to mean that the information is accurate, will apply to your use correctly, or even that the poster's bike runs right with the posted setup. Use it as a guide/starting point only, and look at as many relevant postings as you can before proceeding.


Post your jetting using the template below (copy and paste to your post) and please be as complete as you can. In the Comments section please include any modifications you feel will have a bearing on the jetting, such as cams, accelerator pump mods, bored carbs, etc.



Edit Revision Date:

Main Jet:

Pilot Jet:

Starter Jet:

Leak Jet (if any):

Fuel screw/Setting:




Altitude Range:

Temp Range:

Humidity Range:



OEM 2000 YZ426F(M) Jetting:

Main Jet: 162

Pilot Jet: 42

Starter Jet: 72

Leak Jet (if any): N/A

Fuel screw/Setting: 1.25 - 2.0 turns out

Needle/Position: OBEKR-4

OEM 2001 YZ426F(N) and 2002 YZ426F(P) Jetting:

Main Jet: 162

Pilot Jet: 42

Starter Jet: 72

Leak Jet (if any): N/A

Fuel screw/Setting: 1.25 - 2.0 turns out

Needle/Position: OBEJP-4

Model: 01 YZ426F

Edit Revision Date: 23 Nov 08

Main Jet: 165

Pilot Jet: 42

Starter Jet: 72

Leak Jet (if any): N/A

Fuel screw/Setting: 2 turns out

Needle/Position: JD blue needle/4th ring

Filter: Amsoil/UNI/K&N

Pipe/muffler: FMF powerbomb header/stock muffler/Dr D spark arrester end cap

Altitude Range: 2,500 ft

Temp Range: 70F

Humidity Range: very dry

Comments: Besides the JD jet kit and powerbomb mentioned above this bike also has hotcams exhaust cam installed and an NGK iridium spark plug. Intake port has been deburred and slightly polished, exhaust port has been highly polished. Running 91 octane Chevron pump gas. Runs great.

Model: 2002 YZ426F with Lukes racing 444cc kit (12.5:1 compression)

Edit Revision Date: 11-24-08

Main Jet: 170

Pilot Jet: 45

Starter Jet: stock

Leak Jet (if any): 60 leak jet with a JD bowl

Fuel screw/Setting: 1 to 1 1/8 depending on the weather

Needle/Position: 4th clip (JD red all year)

Filter: UNI/Ready

Pipe/muffler: FMF power bomb/Ti-4 muffler

Altitude Range: 500ft

Temp Range: 40 degrees-85 degrees

Humidity Range: very high most of the year

Comments: Wired acc pump, runs decent on 93 pump gas, runs excellent on 110 leaded race fuel. Twin Hot Cams, fully polished and flowed head, Ti valves. Bike acts like it has fuel injection, no bog or hesitation on the stand or while riding. It does pop just a little like a properly jetted YZF should.

Model: 2001 YZ426F

Edit Revision Date: 12.20.08

Main Jet: 170(JD Jet)

Pilot Jet: 42

Starter Jet: NA

Leak Jet (if any): NA

Fuel screw/Setting: 1.25 Turns Out

Needle/Position: JD Needle Blue - 4

Filter: Twin-Air

Pipe/muffler: FMF Power-Bomb with Ti4 Exhaust Modified(Shortened 3")

Altitude Range: 0-1000

Temp Range: 40F - 100F

Humidity Range: 60% - 95%


Other Mod's were O-Ring Accelerator pump mod. '07 Airbox opened up to increase airflow.

Before JD Jet Kit, The Main Jet was a 175 and had stock needle. It would have initial bog down low.

Model: 2000 YZ426

Edit Revision Date:

Main Jet: 175

Pilot Jet: 42 (stock)

Starter Jet: 72 (stock)

Leak Jet (if any): (stock)

Fuel screw/Setting: stock @ 3 turns

Needle/Position: FMF progressive taper @ 2nd ring

Filter: Moose

Pipe/muffler: FMF Ti-4 w/header

Altitude Range: 0-100 Florida Panhandle (PCBeach)

Temp Range: 45-75

Humidity Range: 75-95

Comments: was 10 by the time I got finished so couldn't turn it up much or ride it. It was harder to start but not bad. idles very nice and throttle response was incredible. I'm hoping it fairs as well under load

Model:'00 YZ426F

Edit Revision Date:

Main Jet: Stock

Pilot Jet: 40 (one size down)

Starter Jet: Stock

Leak Jet (if any): ?

Fuel screw/Setting: Between 1.5 to 2 depending on altitude

Needle/Position: One clip position leaner

Filter: K&N

Pipe/muffler: Stock

Altitude Range: At Sea level, very very lean. Good to 10,000ft, >10k starts to bog due to rich conditions (most riding 4500-10,000 ft)

Temp Range: 50-115 F

Humidity Range: Dry! 0-10% humidity


FreePowerNow, Factory R&D Accel Pump cover, Storm Racing fuel screw

Model: 2002 YZ426f

Timing: YZ

Main Jet: 168

Pilot Jet:45

Starter Jet: stock?

Leak: #58 installed (MOD)

Fuel screw: 1/2 -3/4 turns out

Needle:Yamaha NDJP at #4 clip (1 needle leaner than stock "P")

Air box: no lid, K&N ( I hate cleaning the foam filters)

Pipe/muffler: Stock

Altitude: 10 feet

Temp:current 65

Humidity: 100%

Model: 2001 YZ426

Edit Revision Date: first post

Main Jet: 155

Pilot Jet: 40

Starter Jet: ?

Leak Jet (if any): ?

Fuel screw/Setting: not sure

Needle/Position: 2

Filter: K&N

Pipe/muffler: WR Stock

Altitude: 6-8k

Temp: 30-85

Humidity: 10-40%

Comments: so far seems awesome, but will continue to test....especially up to 10-12k feet.

Model: 2002 WR 426

Timing: YZ

Main Jet: 168

Pilot Jet:42

Starter Jet: stock

Leak: stock

Fuel screw: 2 turns out

Needle:JD red 5th clip

Air box: no lid, 2 stage foam

Pipe/muffler: GYTR head pipe, YZ muffler/DRD spark arrester end cap

Altitude: 12-1,500 ft

Temp:current 80

Humidity: 80-90%

Comments: No grey wire and throttle stop of course. Also added thick o ring to the AP pump arm linkage. Don't have many miles on it yet but so far it starts and idles excellent and is very explosive. Will experiment with the JD blue needle and 170 main this fall when it cools off here in Michigan...

Edited by un chained

2000 yz426

45 pilot

158 main

needle up 1 from stock

elevation 8150'

fuel screw 1 1/2 turns out

temp and humidity fluctuate a great deal depending on time of day

comments: smooth power delivery, let a couple of friends ride it and they swear its smoother than the wr450 and yz450 each of them ride respectively

Model 2001 yz426f

Main jet 175

Pilot jet stock

Leak jet stock

Starter jet stock

Fuel mix screw 1 5/8 turns out

Needle stock

Filter /foam with wd40 coating

Pipe/muffler stock

Altitude 1000-3000 feet

Temp 65°-85°

Humidity dry /foggy morning

Idle at 1050

Bike runs really good no ajustments needed for me

Year: 2002
Model (400 - 426 - 450): YZ 426
Cam Timing (WR/YZ): yz
Main jet: 168
Pilot Jet: 48

Starter Jet: Stock 72
Fuel screw (turns out): 3/4
Needle Model/Clip position: Y356  4th
TPS Connected (Y/N): Y
Airbox Snorkel/Lid (on or off): off
Airfilter Brand: UNI
Exhausticon1.png Brand:  FMF Silencer

Average Altitude: 0 - 100m
Average Temperature: WInter 65 Summer 110

Humidity: Dry
Degree of Satisfaction (0-10): 9/10
Additional Mods/Comments: Gearing 14/47, IMS 3 Gal.

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