2008-09 YZ450F User Jetting Database

Finally got my 08 dialed in for the Pro Circuit Ti-4 pipe. All the jets were changed from stock settings. Here is what i ended up with and the bike runs perfect for Sea level/So.Cal tracks. 165 main/from160------43 pilot/from45----------NFPP needle/from stock--------50 leak jet/from 55----2 turns on the mixture screw.:confused:

I need to same info, anyone have the #'s out there for us stock people? I'm at sea level also. My Wife bought me an 08 for Christmas and it doesn't like to start very easy.:eek:

In the Australian Dirt Bike mag shootout, they used the following

Bike: 08 YZ450

Main Jet: 158

Pilot Jet: 45 (stock)

Starter Jet: stock

Needle: NFPR (stock)

Clip: 4th

Leak: stock

Fuel screw: 2.5 (stock)

March 08 Motocross Action Mag

Bike: 08 YZ450

Main Jet: 160

Pilot Jet: 45 (stock)

Starter Jet: stock

Needle: NFLR (stock)

Clip: 3rd

Leak: 55

Fuel screw: 2-3/8

Comment "Apart from fuel screw adjustments, the YZ450F ran like a top."

My settings (sea level, hot, high humidity)

All stock - starts & runs okay (usual bog off idle and slight popping on throttle chop). It only has 3 hours, so will fine tune with a couple more hours

Bike: 08 YZ450

pipe - Yoshimura RS

sea level, temp 10-15 degrees C

Main Jet: 165 (tried with 160 and 170 - no difference felt)

Pilot Jet: 48

Starter Jet: stock

Needle: NFLR stock

Clip: 3rd

Leak: 50

Fuel screw: 0

Ok - after the pipe came in the decel pop was heavy and annoying. Advice that I got here was 48 pilot, 50 leak and needle up one groove. Got the jets yesterday...

the swap from all stock carb DONE yeasterday. Oh, and I have Ride Eng fuel mixture screw. But it works funny.

Now I have anoying bog (to the extent engine dies at sharp throttle opening) , same (if slightly less) decel pop...

and the funny thing is the engine works with th fuel screw fully in! it continues to work with no audible difference till 2,5 turns, then rpm falls...

on stock carb the same screw worked on 2,5 turns, and rpm started to fall at about 0,5 turns....


I have spent alot of time on jetting this bike, with these specs the bike is crisp off the bottom and very strong in the midrange and no popping at all!

42 pilot

165 main

nfpp needle 4th position

55 leak jet

1/-1/2 fuel screw

Model: 2008 yz450f

Main Jet: 160

Pilot Jet: 48

Starter Jet: Stock

Leak Jet : 55

Fuel screw/Setting: 1 3/4

Needle/Position: Stock

Air box/Filter: Twin Air

Pipe/muffler: Stock

Altitude: 600-1600

Temp: 75-90 degrees

Humidity: varies

This jetting works awesome for me i have great power everywhere with NO bog or hesitation. I also have done the O-ring mod with a 1/8 thickness o-ring, installed a boysen quickshot accelerator pump cover, put in a boysen powerblade on the air boot, and cut out the screen on the air filter cage. Bike RIPS now!

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:

Fuel screw/Setting:




Altitude Range:

Temp Range:

Humidity Range:



OEM 2008 YZ450F(X)

Main Jet: 160

Pilot Jet: 45

Starter Jet: 72

Leak Jet: 55

Fuel screw/Setting: 1.5-2.0 turns out

Needle/Position: NFLR-3

2008 YZ450F

Main Jet: 165

Pilot Jet: 45

Starter Jet: 72

Leak Jet (if any): 55

Fuel screw/Setting: 1.5-2.0 turns out

Needle/Position: NFLR-3

Alt: Sea level - 500 ft (Seattle, WA)

Pipe: Dr D full system, stainless.

Air filter: Stock

Comments: Still pops on decel, may try raising the needle 1 clip, and one size bigger pilot jet. This bike is VERY fast up top. I mean VERY fast. I thought my 04 was fast, but this bike with a DR D pipe blows the 04 away. It feels like I could put 1-2 less teeth on the rear and it will pull it easily.

2008 YZ450F Minnesota

170 main jet

45 pilot

55 leak jet

stock needle

Fuel Screw 1.5-2

It seems to run great above 60 degrees, pops in cooler conditions needs more fuel in the middle.

Bike: 2008 YZ450

Main Jet: 160

Pilot Jet: 45 (stock)

Starter Jet: stock

Needle: NFLR (stock)

Clip: 3rd

Leak: 55

Fuel Mix: 2 turns out

Stock 08 Pipe with PMB. No popping on decel fires on first kick when hot.

Riding in California sea level - 1500ft 60-80 degrees

Model: 2008 YZ450

Edit Revision Date: 1/12/08

Main Jet: 168

Pilot Jet: 48

Starter Jet: STK

Leak Jet (if any): STK

Fuel screw/Setting: 1.25

Needle/Position: NFLR - 3rd clip (STK)

Filter: Stock

Pipe/muffler: Pro Circuit T4 Slip on

Altitude Range: 0-1000'

Temp Range: 65-90F

Humidity Range: ?? Dry Desert

Comments: I tried 165 main 4th clip and 45 pilot but it was a bit lean. With the above setup the bike starts easier and runs better. Although, typical off idle bog if you slam it open, I plan to play with the AP spring and leak jet.

Model: 2008 YZ450 stock pipe

Edit Revision Date: Feb 09

Main Jet:160 cold/155 warm

Pilot Jet: 42

Starter Jet: STK

Leak Jet (if any): STK

Fuel screw/Setting: 2 1/4 cold or 2 out warm

Needle/Position: NFLR - 2nd from top(STK)

Filter: Stock

Pipe/muffler: stock w/quickshot Altitude Range: 2370-2500ft

Temp Range: 30 up to 90F

Humidity Range: ??

Bike starts better than ever before.Quicker response then ever. Will have update as soon as new tires and clutch installed asap and a real ride is taken at about 30-40F.May put needle back to stock 3rd position.

Main Jet 160

Pilot Jet 45

Leak Jet 55

Stock Needle Position 3

Fuel Screw Turns 1-1/2

Altitude 5-7k

Temperature F 50

Plug Condition white

Result No Complaints

Stock 2008 YZ450 w/ PMB Spark Arrestor

Its running a bit lean but when I change the clip to 4 it "lopes" at low throttle. Just bought the bike new Nov 08 so havent had a chance to experience warm weather jetting yet. I suspect it will be pretty close.

Bike - YZ450f 2008

Main Jet - 170

Pilot Jet - Stock

Leak Jet - Stock

Needle - JD Blue Neede Position 3

Fuel Screw - Merge racing Turns 1-1/2

Altitude - 0 - 3000f

Temperature - 27-36C'

The bike has more power and speed than ever and no popping at all.:ride:

Model: 2009 yz450f

Edit Revision Date: 6/21/10

Main Jet: 165

Pilot Jet:stock

Starter Jet: stock

Leak Jet:stock

Fuel screw/Setting: 2 1/4 out

Needle/Position: stock nedle 4th position

Filter: twin air

Pipe/muffler: fmf 4.1 with megabomb

Altitude Range: 700ft

Temp Range: 80-90°F

Humidity Range: uhhhh sunny southern CA

Bike starts second kick cold, first kick hot. After I put on the pipe the bike felt like it ran strong just had a lot of decel pop. Turned to fuel screw to 2 1/4 out from 1 1/2 stock and raised the clip and popping/backfireing is all gone once the bike warms up and it has good throttle response.

Model: 2009 YZ450f

Edit Revision Date:

Main Jet: 160 stock

Pilot Jet: 45 stock

Starter Jet: stock

Leak Jet: R&D powerbowl / AP / stiffer spring

Fuel screw/Setting: Zip Ty screw / 2 out

Needle/Position: NFLR 3rd stock

Filter: UNI

Pipe/muffler: Megabomb / 08' stock can w second baffle removed / PMB

Altitude Range: 700'

Temp Range: 70*

Humidity Range: 60%

With my wideband idle is 14.2-13.8 progresses smoothly down to 11.5 throghout the throttle range. The stock jetting is wonderful on this bike. Starts on first kick warm and cold; I love this bike.

Model: 2008 YZ450F

Edit Revision Date:

Main Jet: 160 (Stock) Going to try a 165 if it stays under 60 deg. this weekend

Pilot Jet: 48

Starter Jet: Stock

Leak Jet (if any): Stock

Fuel screw/Setting: Works Connection Screw 1 1/2 out

Needle/Position: Stock

Filter: No Toil

Pipe/muffler: Stock Header, FMF Powercore 4

Altitude Range: 0-2500

Temp Range:55-80

Humidity Range: Very little/ Northern CA

The 48 pilot made a huge difference in throttle response and very little popping on decel now.

Model: '09 YZ450

Edit Revision Date: 1-5-11

Main Jet: 165

Pilot Jet: Stock

Starter Jet: Stock

Leak Jet (if any):

Fuel screw/Setting: 2 1/4 turns out

Needle/Position: NFLQ-4th from top

Filter: Stock Filter/YZ250 filter cage

Pipe/muffler: MRD Full System

Altitude Range: 500-3000 ft.

Temp Range: 50-90 degrees

Humidity Range:


Edited by FZ1426

Model: 2009 YZ450FY

Edit Revision Date: 05/12/11

Main Jet: 160 (Stock)

Pilot Jet: 45 (Stock)

Starter Jet: n/a

Leak Jet (if any): 55 (Stock)

Fuel screw/Setting: 2 1/2

Needle/Position: NFLR-3 (Stock)

Filter: Twin Air

Pipe/muffler: FMF Q4

Altitude Range: 2500

Temp Range: 70 Degrees

Humidity Range: Low/Dry

Comments: Bought the bike second hand and trying to get a "Stumble" or rough mid-range cleared up. I have dropped the clip position to both the 4th and 5th position and have NOT cleared it up. Gonna try to raise it to the 2nd this weekend.

Edited by flac5364

Model: 2008 YZ450F

Edit Revision Date: 07/14/11

Main Jet: 162

Pilot Jet: 45 (Stock)

Leak Jet (if any): 55 (Stock)

Fuel screw/Setting: 2 1/2

Needle/Position: NFPP-3

Filter: No-Toil

Pipe/muffler: FMF PowerCore

Altitude Range: 5500

Temp Range: 80 Degrees

Humidity Range: Low/Dry

Runs great, had stock 160 main on other bike (have two of the same model), major decel pop and raced at El Centro sea-level but it burned up crank (too lean). Rebuilt with big-bore and plan to run 165 main in it in the future, maybe go to JD red needle on it, but JD seemed too rich with stock cylinder.

Edited by NewMexican
Update 1/2 step richer Needle P/N info

Model: 2008 YZ450f

Main Jet: 165-168

Pilot Jet: 48

Starter Jet: Stock

Leak Jet: Stock

Fuel screw: 1 1/2 - 1 7/8

Needle/Position: Stock, Stock

Filter: Twin Air

Pipe/muffler: Stock with Lexx endcap

Altitude Range: 800'-1,000'

Temp Range: 70-95 F

Humidity Range: 95%-100% Freaking humid (Wisconsin)

Comments: My bike runs crisp with this jetting and starts 2-3 kicks cold with choke and 1-2 kicks hot with hot start. Very slight pop on decel.

Edited by ttr250dude

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