YZ250f Jetting 01-09

[motofreak0592]

I found this in the September 2009 issue of Motocross Action Magazine. I hope its useful to some people.

YAMAHA YZ250F JETTING:FROM 2001-2009

(9/2009)

As the original 250cc four-stroke of the modern era, the Yamaha YZ250F has the most development and refinement time of any bike of the track. Its jetting specs have evolved slowly over the last nine years (and the 2009 model isn’t all that different from the 2001 YZ250F). This is testimony to Yamaha’s thorough test program. They are very good at getting it right the first time then making it better with each passing year.

As with every jetting guide, there are caveats about temperature, altitude, riding style, hpo-ups, and personal taste. Our numbers are suggested starting points for motocross racers (the stock jetting, when changed, is included in parenthesis). The fine tuning is still up to you.

2001 YAMAHA YZ250F JETTING

Main: 175

Pilot: 42

Needle: OBELP

Clip position: 4th from top

Fuel screw: 2 turns (1-1/2 stock)

Leak jet: 95 (105 stock)

2002 YAMAHA YZ250F JETTING

Main: 178 (162 stock)

Pilot: 40

Needle: OBEKP

Clip position: 4th from top (4th stock)

Fuel screw: 2 turns (1-5/8 stock)

Leak jet: 90 (100 stock)

2003 YAMAHA YZ250F JETTING

Main: 178

Pilot: 42 (40)

Needle: OBELP

Clip position: 4th from top (4th stock)

Fuel screw: 2 turns (1-5/8 stock)

Leak jet: 100

2004 YAMAHA YZ250F JETTING

Main: 180

Pilot: 42

Needle: OBEKR

Clip position: 4th from top

Fuel screw: 1-1/2 turns out

Leak jet: 90

2005 YAMAHA YZ250F JETTING

Main: 180 (182 stock)

Pilot: 42

Needle: OBELR

Clip position: 4th from top

Fuel screw: 2 turns (1-3/4 stock)

Leak jet: 90

2006 YAMAHA YZ250F JETTING

Main: 180 (178 stock)

Pilot: 42

Needle: OBELQ

Clip position: 3rd from top

Fuel screw: 2-1/2 turns

Leak jet: 80

2007 YAMAHA YZ250F JETTING

Main: 180 (178 stock)

Pilot: 42

Needle: OBEPQ

Clip position: 3rd from top

Fuel screw: 2 turns out (1-1/2 stock)

Leak jet: 80

2008 YAMAHA YZ250F JETTING

Main: 178

Pilot: 42

Needle: NFPR

Clip position: 5th from top

Fuel screw: 2-3/8 turns

Leak jet: 70

2009 YAMAHA YZ250F JETTING

Main: 178

Pilot: 42

Needle: NHKR

Clip position: 4th from top

Fuel screw: 2-1/2 turns out (2 stock)

Leak jet: 70

[spinner38]

i found it helpful! thanks! makes an easy resource when changing needles and such

[roncar12]

Has anyone experimented with putting a larger pilot JET in a 2005 YZ250F?  I had some issues with mine a short while ago when it sat for a while.  I had to pull the bowl, clean the JET, bowl, etc. without having to completely pull the carb.  After I did that, it kicked over 2nd kick no problem however not a week later I had it at the track and had to kick it a lot more to get it to crank.  I haven't as yet checked the valve alignment, that is the next project because I'm having to run the idle way up to crank it then turning it back down to a normal setting to warm up.  Hopefully, I will be able to do that before I ride again.  I already have an aftermarket fuel/air screw in it so I will be turning it to the 2 setting, it is still at the stock setting as well.  I have started completely draining the tank and letting it run totally dry so as not to have it sit with gas just standing in the carb and engine.  That has seemed to help.

 

Any thoughts would be greatly appreciated before I start monkeying around with it. 

[dimebag828]

Great information, none of the links I could find about stock jetting are still working websites. I have a 2002 YZ250F and I currently have a JD carb kit following instructions in it this is how mine looks for my elevation (1000ft).

Main: 185

Pilot: 42 pilot - I assumed to use a 42 since JD carb kit was based off 2001 stock pilot

Needle: JD blue 

Clip position: 5

Fuel screw: 2 turns (1-5/8 stock)

Leak jet: 35 (QS3)

[Tywon Aaron]

Hey im a owner of a 03 250f yz I purchased a carb rebuild kit for but the jets doesn't match the spec . That are needed my 1: main jet is 170 my 2: pilot 48 an my 3: starter jet doesn't have any specifications to tell its size I can't check the leak jet its not moving at the moment an I dont want to brake it so I put a wire through to check an an air hose to clean for the time being,  what can't I do about this , can this be a reason my bike turns over but not starting ? Thanks in advance.

 

[mlatour]

2 hours ago, Tywon Aaron said:

I purchased a carb rebuild kit for but the jets doesn't match the spec

Skip questionable 'kits', buy genuine / OEM replacement parts, more expensive yes but do it once, do it right.

FCR carburetors can be finicky on cleaning method and wear items, read the do's and don'ts in the topic linked below:

link: https://thumpertalk.com/forums/topic/1291644-2005-yz250f-fcr-carb-maintenance/

 

 

2 hours ago, Tywon Aaron said:

can this be a reason my bike turns over but not starting ?

Could be different issues and/or a combination of many 

but aside from a completely plugged up carburetor,

by far the number one reason 4-stroke MX race bike engines become hard to start

is compression loss past a mis-adjusted or worn out valves/valvetrain.

 

 

Edited September 20, 2021 by mlatour

[Tywon Aaron]

Thanks for the information very helpful