2000-02 YZ426F User Jetting Database

15 replies to this topic
  • Scotty426

Posted June 06, 2005 - 09:59 PM


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.

  • Chills

Posted July 07, 2005 - 10:16 AM


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...


Posted December 14, 2005 - 12:25 AM


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:

  • spinblue

Posted July 21, 2006 - 11:31 AM


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.

  • yamaboy23

Posted July 24, 2007 - 07:44 AM


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?????

  • grayracer513

Posted September 22, 2008 - 08:03 PM


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

  • whyzee426F

Posted November 23, 2008 - 08:33 PM


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.

  • 642MX

Posted November 24, 2008 - 09:04 AM


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.

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  • Thrash1

Posted December 20, 2008 - 08:05 AM


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.

  • rmx

Posted January 07, 2009 - 03:07 PM


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

  • DrThumper

Posted February 24, 2009 - 01:07 PM


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

  • Drover

Posted September 16, 2009 - 03:51 PM


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%

  • mtnadventurerider

Posted September 30, 2012 - 05:08 PM


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.

  • un chained

Posted June 27, 2013 - 07:35 AM


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, June 28, 2013 - 07:29 AM.

  • rogo1

Posted August 12, 2013 - 03:03 AM


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

  • Kqwackey101

Posted May 08, 2014 - 08:17 PM


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

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