Need Re-Jetting Help? ~YFZ450 Jetting Guide Inside~

350413 Views 646 Replies 253 Participants Last post by jordanmolinaro98, 27 d ago

screamin96

Discussion Starter · Sep 12, 2003 (Edited by Moderator)

Our very own "edge" has compiled this great little jetting guide for all of you who are having problems, or need a starting point before you attempt to re-jet your YFZ450's FCR carburettor. Thanks, great! :tup:

This is a pretty basic outline for jetting on the YFZ450. These settings are for sea level if you are anywhere from 1500ft to sea level these settings should be very close to right on. Anything above 1500ft should lean the settings accordingly. Also, as a good adjustment, you should raise the idle by roughly 10 steps on the knob. The dealers set the idle way too low and that is a big cause for stalling these things.

Stock YFZ off the showroom floor: 158 main 42 pilot #3 clip on needle 2 turns the mixture
Stock YFZ with a much-needed re-jet: 168 m 45p #4 clip 2 turns mature
YFZ w/baffle out same as above
YFZ w/baffle out and lid off: #5 or #6 clip same settings as above.
YFZ wipe and lid on 168m 45p #5 or #6 clip should be very close

Now, for this next set of jetting, you will need to buy either a James Dean jet kit(www.jdjetting.com) or a GYTR jetting kit from your local dealer.

YFZ w/pipe and lid off GYTR needle #4 clip 168m 45p 2.5 turns mixture screw.
YFZ w/pipe and lid off JD blue needle #3 168m 45p 2.5 turns mixture screw.

The above settings are somewhat rich but this engine craves tons of fuel and tons of air to make big HP. I have yet to foul a plug running the JD Jetting settings on my YFZ with a Sparks pipe and the YZ exhaust cam. Also, all the pipes out for the YFZ are going to be pretty close to the same jetting-wise so this FAQ should get you pretty close. Again, these settings cannot be a sure thing across the board but these are VERY close guidelines that you can use to get your YFZ450 to run as it should. I hope this helps get rid of some of the jetting posts that we see every day. If you have any questions about how to alter your jetting to dial it in exactly please ask the questions here so that we can all learn from your testing.

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601 - 620 of 647 Posts

jonathangalindo

· #601 · Jan 28, 2012

yfz450

I have this problem on a yfz450 its all stock, but the only thing I put on the bike is ESR filtter and I took my stock air box out. I have a stock exhaust but the bike is running like crap.. Do i have to re-jetted? or what can I do to fix the problem. Thank you.!:shrug:

Bowtie

· #602 · Jan 28, 2012

Yes you need to rejet

Garth9411

· #603 · Feb 17, 2012

Garth9411 said:
08 450 with a 478cilnder works big bore,full racing velves, full T4 PC pipe,hot rods crank and rod oem size,stage 2 hotcams ,air box lid goen,msr air screw ,hi flo water pump, dina fs programabul ecm,it runs like a animal the way I have it now I cant say for sheer cuz it was 2 years ago now I bilt it but I plan to clean the carbs soon befor I put the TJD track and ski kit on for the winter so il repost then what I have in it now, I do know the main jet is one of the biggest u can get for these carbs...I do rember that. Any input on were I really should be jeting this beast would be great, like I said it runs like a animal and has no dead spots and idals perfict, how would you have set this up ?? I just wnt to see what someone else would of done. Thanks !

Any takers on ideas

Taiq

· #604 · Feb 27, 2012 (Edited)

i have a yfz 450 2008, lid on, big gun slip on, main 160, pilot 42 mix screw 2. its like the bike is running rich cause my spark plug is black.
should i go to a 158 main.
i'm also 6.6 ft below sea level

when i go easy on the gas, it shuts off at 2100rpm, but if i hit it, every thing goes fine.
it's rich right?

Hayter11

· #605 · Feb 27, 2012

I am using a 170 main, needle on the first clip. it seems to be running just slightly lean. If I move the main down to a 168 and the neddle down to the 2nd or third clip do you think this would help? Thanks

codyfelker

· #606 · Mar 29, 2012

06 yfz

I have a 2006 yfz 450, i cant get this thing running right to save my life. i cracked my high comp piston the other day and just put in a cylinger works big bore kit. i was wondering what your opinion on how to jet it would be. Its a +3mm 478cc bore with a vertex piston. not sure the compression ratio. i have a yoshi slip on and a vortex filter with the lid on. . also when i bought the bike it was jetted very high. it has a 192 main 58 pilot and 4th clip on the needle. that seems really high to me.and it runs like crap
thanks

+3mm 478cc big bore
vertex filter
lid on
yoshi slip on

Bowtie

· #607 · Mar 29, 2012

codyfelker said:
I have a 2006 yfz 450, i cant get this thing running right to save my life. i cracked my high comp piston the other day and just put in a cylinger works big bore kit. i was wondering what your opinion on how to jet it would be. Its a +3mm 478cc bore with a vertex piston. not sure the compression ratio. i have a yoshi slip on and a vortex filter with the lid on. . also when i bought the bike it was jetted very high. it has a 192 main 58 pilot and 4th clip on the needle. that seems really high to me.and it runs like crap
thanks

+3mm 478cc big bore
vertex filter
lid on
yoshi slip on

Based on your altitude of 2000 feet, you need to start with a 180 main, 48 pilot and the clip on the 3rd from the top to start. Ride it and see how it does.

Bowtie

· #608 · Mar 29, 2012

Hayter11 said:
I am using a 170 main, needle on the first clip. it seems to be running just slightly lean. If I move the main down to a 168 and the neddle down to the 2nd or third clip do you think this would help? Thanks

Need more info, need to know what mods you have, what's the altitude you ride at, what pilot jet do you have in it?

Ironfists

· #609 · Mar 30, 2012

06 YFZ450

I have a 06 YFZ450, bought a HMF performance slipon. Also bought the HMF jet set along with it. What do you think jets I should use?
Around the Phoenix area. No other mods airbox on.
HMF recommends 170main and 48 pilot.
What are your thoughts?

Bowtie

· #610 · Mar 30, 2012

The 48 pilot is probably to big, but the 170 is right on. you might have to turn the fuel screw out about a 1/4 turn as well.

Garth9411

· #611 · Mar 31, 2012 (Edited)

Garth9411 said:
08 450 with a 478cilnder works big bore,full racing velves, full T4 PC pipe,hot rods crank and rod oem size,stage 2 hotcams ,air box lid goen,msr air screw ,hi flo water pump, dina fs programabul ecm,it runs like a animal the way I have it now I cant say for sheer cuz it was 2 years ago now I bilt it but I plan to clean the carbs soon befor I put the TJD track and ski kit on for the winter so il repost then what I have in it now, I do know the main jet is one of the biggest u can get for these carbs...I do rember that. Any input on were I really should be jeting this beast would be great, like I said it runs like a animal and has no dead spots and idals perfict, how would you have set this up ?? I just wnt to see what someone else would of done. Thanks !

:shrug:Ok got the carb off and cleaned it out checked the jetting and i have.
main is a 210 ,45 pilot, 2nd clip,air is 2 1/4 turns.she ran great befor i cleaned the carb out and added a R&D power blow and pump accelerator , now i can just get it to ideal some what to par but it just cuts out if i punch it. The accelerator pump leak jet is set the stock leak jet size. Has anyone tryed these two products? ? If so how did it change ur jetting? Like i said it ran great befor i cleaned the carb out and added the power blow and pump accelerator. Now i cant figer it out iv messed with it off and on for a couple weeks now on my free time but no luck yet Any help would be grate and thanks in advance!!! Garth:shrug:

airbornemattyd

· #612 · Apr 1, 2012

i need help

i just bought a 04 yfz 450. it is bored over .20 has a full hmf exhaust, open k&n airfilter. it has a stop jet in it. you can hear the compression, and it almost starts but i know it needs to be rejetted. i just don't know what size jet i am in need off. anyone think they can help??

tomtomH

· #613 · Jun 2, 2012

i have a 07 yfz450 full two brothers exhaust no air box lid it dies when u stab the gas it has 45 68 needle 3rd clip down 650ft elevation should i try the zip tie trick im going riding tomorrow need help please

flavtfan

· #614 · Jul 4, 2012 (Edited)

I have a 2007 yfz with FCI, no air box, Full Jardine RT99, cammod, zip tie mod. What should I be jetted at for about 1800-2000 feet(Vegas, temps around 90) My current jetting is 170m, 45p, 35 Leak, NDSR needle 3rd clip, AF screw 2 turns out. When I hold it at HT while sitting still it kind of stumbles/sputters a little and isn't that smooth, also when i stab the throttle to about HT and let of quick i get a pop and sometimes it pops while giving the throttle a quick stab to HT. Am I lean on the pilot? Lean on the Needle? It starts and idles pretty good and is smooth on idle. Should I try 48p and 4th clip?

mbogosia

· #615 · Jul 5, 2012

airbornemattyd said:
i just bought a 04 yfz 450. it is bored over .20 has a full hmf exhaust, open k&n airfilter. it has a stop jet in it. you can hear the compression, and it almost starts but i know it needs to be rejetted. i just don't know what size jet i am in need off. anyone think they can help??

Post up what is currently in there and then I am sure someone can help. Also post up the altitude where you are and temperature range.

Bryant22

· #616 · Jul 31, 2012

hi there im new to this site and new to working on the carbs on yfzs i have an 04 and have a few questions, Where is the pilot jet? where can you access the needle to adjust the clip postion? i have the carb loose and i can get to the main jet under the 17 mm nut just need some help on the pilot and needle any help will be greatly appreciated

thek5king

· #617 · Aug 22, 2012

Help with Jetting

My buddy has a bone stock 2008 Yfz 450..We are putting a full Big Gun Evo exhaust on it and pulling the lid this weekend. Can someone recommend the jet setup so I dont have to buy a whole kit..We ride at 1000 ft elevation.. Thanks Trent

cajuncritter

· #618 · Sep 1, 2012

I have an 06 yfz450, it pours gas out of da tattletale on da carb. bowl sometimes, not often, low speed jet ?

Geko469

· #619 · Sep 10, 2012

04 YFZ 450

Hello, Ive been searching this site, and kinda have a good idea what I need to start with. But was going to ask what you might think. Im the 3rd owner of a YFZ450. Im told the 1st owner put a cam and HMF exhaust on to, 2nd owner not mechaically inclinded, so didnt ask alot about bike, but it has stickers of boyesen and wiseco. Im in Hillsboro, would be riding at sealevel, and maybe up to Browns(about 1500ft). Its popping bad on rev, and has the bod issue. What main and pilot jets you think I should try? Do I need to change the leak jet? thx

jcrinella

· #620 · Sep 26, 2012

2004 yfz to rich

i have a 2004 yfz, its running way to rich there is currently a 172 main in there with a 42 pilot, im running a biggun slip on with the air box lid on but with vents instaled. i am getting a lot of back firing and when the throttle is tapped and let out it is throwing a flame about 8 inches. im at 853ft above sea level. what should i change my jetting to?

601 - 620 of 647 Posts