1998-99 YZ400F User Jetting Database

4 replies to this topic
  • 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 thread. 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 1998 YZ400F(K) and 1999 YZ400F(L)Jetting:

Main Jet: 175
Pilot Jet: 45
Starter Jet: 65
Leak Jet (if any): N/A
Fuel screw/Setting: 1.5 - 2.5 turns out
Needle/Position: OBDVR/4

  • DeeCee

Posted January 11, 2009 - 06:14 PM


Model: 1998 YZ400f
Edit Revision Date:
Main Jet: 170
Pilot Jet: 45
Starter Jet: 65
Leak Jet (if any): N/A
Fuel screw/Setting: 1.75
Needle/Position: JD Jetting Red Needle/2
Filter: Stock
Pipe/muffler: White Bros E2
Altitude Range: Sea level to 100m
Temp Range: 20 - 50 deg C
Humidity Range: 80-95%

Comments: The bike is ridden in the UAE desert. Summer temperatures range 35-50 deg C, winter 20 - 35 deg C.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • markk21

Posted February 02, 2009 - 07:14 PM


Edit Revision Date:
Main Jet: -stock
Pilot Jet: -stock
Starter Jet:???(what is this) Im a honda ATV man and im not sure what this is.
Leak Jet (if any): (???)
Fuel screw/Setting:2.5turns out
Needle/Position: stock
Pipe/muffler:FMF slip on
Altitude Range:516 above sea level
Temp Range: - 30F-100F
Humidity Range:40-100

Comments: friend of mine got this bike for the right price- and im not very sure about the CR carbs. I was wanting to know what everyone is jetting there carbs to around the midwest area or east coast. i need jet sizes needle position and air-fuel mixture.
any info would be great guys. Thank you very much.

mark knox
centralia illinois

  • 400f mech

Posted February 21, 2009 - 08:35 PM


Edit Revision Date:
Main Jet:185
Pilot Jet:45
Starter Jet:65
Leak Jet (if any):
Fuel screw/Setting:1.5-2
Filter:twin air
Pipe/muffler:fmf powercore 4 slip on
Altitude Range:850-950
Temp Range:-10f-90f
Humidity Range:40-100

Comments:Also running hotcams, and 94 fuel, live in ohio so the weather is never the same and allways seems to work

  • Deadend

Posted August 02, 2011 - 12:57 PM


Model: 1998 YZ400F
Edit Revision Date: ?
Main Jet: 160 ran (should have been 162 - read comments below)
Pilot Jet: stock
Starter Jet: stock
Leak Jet (if any):
Fuel screw/Setting: 1.5 ish
Needle/Position: middle
Filter: Pod Filter
Pipe/muffler: White Bros w/ USFS Sparky
Altitude Range: 7800 - 9100
Temp Range: 62 - 80 (ambient)
Humidity Range: 30% - 100% ( thunder storms, rain, hot sun all in one day )

comments : I ended up running a 160 main jet. This was just marginally lean, but i didn't have a 162 with me. The plug looked good after 1hr and 10hrs of riding on it, so it wasn't a danger, but there was a small amount of popping on heavy decell

Also : Running CA "May Contain Ethanol up to 10%" 91 octane pump gas (Shell and Cheveron )

Related Content


Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

Should I buy this bike? help....... by Numsa Hul

Dirt Bike   General Dirt Bike Forums   What bike should I buy?
  • * * * * *
  • 10 replies

BIGBORE FOR YZ450F 2006? by Taattie94

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 3 replies

Megabomb Fitment by 288yz450

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 1 reply

The "going back to the other darkside" adventure... by Monk

Dirt Bike   Make / Model Specific   KTM   250/350/450/505 SX-F & XC-F (4-Strokes)
  • Hot  113 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.