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Discussion Starter #1
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 rougly 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 mixture
Stock YFZ with a much needed re-jet: 168 m 45p #4 clip 2 turns mciture
YFZ w/baffle out: same as above
YFZ w/baffle out and lid off: #5 or #6 clip same settings as above.
YFZ wpipe 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 for sure thing across the board but these are VERY close guidelines that you can use to get your YFZ450 to run like it should. I hope this helps get rid of some of the jetting posts that we see everyday. 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.
Thank you,
Isaac
 

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Discussion Starter #2
I am not sure if you are asking what needle I was talking about in the first bunch of settings?? That is with the stock NCVR needle that comes in the carb stock.

The GYTR kit has a NCVQ needle in it. That needle is almost identical to JD"s red(leaner) needle. So, if you would look at it from the perspective that the GYTR needle is going to be about two clips leaner than the BLUE JD needle or 1 clip leaner than the RED needle. I hope this answers your question.
 

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Discussion Starter #3
PAH,
The further you go from Sea Level the leaner you get. Or the higher the elevation the smaller number on the jets.
Isaac
 

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Well thanks Edgerat!! :D

I finally made it to the shop to get a couple of jets, and got the baffle out, lid off, and cam mod,put the 168 main in, 45 pilot, moved the clip on the stock needle down to the 5th position. And all I can say is WOW :O its almost like I bought a whole new bike for the $8 bucks the jets cost me. :lol


Anyone that has not done this yet I say DO IT!!

The POWER is great!!! :yfz
 

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By the way I am at 2000ft and it is 85-90 degrees here.

It might be a little rich but oh well it feels like lots of power everywhere, no stumbles or boggin at all!!!!
 

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Can we get some jetting specs in here with an aftermarket filter like K&N or the GYT-R dual stage? I assume that it would be different from stock because of the lower resistance to the incomming air.
 

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Hey YFZdream, don't go that high yet. I have the same mods and also 15 tooth and heavy modded stock muffler. I have the 45 pilot and tried a 178 main and even though the bike pulled it seemed to have a little stumble. I would stay around a 172 main with the 45 pilot maybe a 170 with baffle in. If you are going on a trip, bring the jets. A 6mm and an 8mm socket. 9 and 10 will work also, just to have. You will need a wrench for the big plug under the bowl. A 1/4 drive socket a 6mm will get the main out. If the jet takes a long tube with it dont be afraid. Bring an adjustable wrench so you can separate the jet from the tube. the tube is 8mm, i think. Its best to put the tube back in first then the jet. that may be too hard. So put the new jet on the tube and put the assembly back in while holding the throttle open. This will keep the needle from getting jammed up. snug up the jet and put everything back. Before you do the jet change, race a buddy who is close to you, tie to 4 bikes win or lose. Then you can do the same after the jet change to see the difference. Stay in the range of 168 to 178 on the main, I think you will fall between those #'s. Oh, and have fun!!!!
 

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Originally posted by z-hindle@Nov 5 2003, 10:45 AM
Hi everybody!!!
I've a complete curtis spark pipe and i want to jet my bike but i don't know i'm at what sealevel??????
know i've  172 main and teh rest is stock!!!!
please help me!!!
i'come from québec canada!!!!
thanks!!!
mike
from canada eh?! :lol sorry man i had to. my girlfriend is actually from toronto and im a hockey fanatic so nothing wrong with canada.

anyway....
i would first find out what elevation your at. if your at sea level or below 1500 ft i would go with
48 pilot
175 main
1.5 turns out on screw
gyt-r needle 4th clip

now this is with a k&N filter and lid off and cam mod
 

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Not an expert but you sound like you are to rich.

Personal experiance: I had my jetting spot on and then put the air box lid back on this weekend for a Harescramble and it did all the things you are discribing.

Conclusion too rich...

Just my .02 you might try a smaller jet
 

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Pahrump,

My first post and it's a beggin'

Could you please send me a copy of those JD jetting instructions as well? :lol

Thanks,

[email protected]
 

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Sent the instructions.

But folks realize these just tell you how mecanically to jet, not how to actually dial the bike in with jet sizes.

Scott
 

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Yeah, I figured that... I was more interested in whether or not there were any nuggets in there that aren't in the Service Manual.

Thanks for sending it. :lol
 

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Would you also please send me the jetting instructions?

[email protected]

I have a GYT-R full exhaust system, I am getting a UNI pro design intake set-up, and want to run it with the air lid off. I live in Arizona if it helps.

Any info will be greatly appreciated!!!!

Thanks Guys!
 

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OK fellas I will send you the JD instructions but to everyone else let me make this clear these just tell you mechanically how to jet, not how to dial your bike in. OK

Scott
 

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this jetting stuff is confusing....

how do you know what to change and to what setting?
i know that it depends on if you have a pipe/intake/lid off/what not....but how do you know? is it something you experiment with? something you are told or what?

say that i have my lid off and baffle out. how do you know that they are as what is listed on the first page?




sincerely,
confused.
 

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hey my bike is stock now and im geting my hmf in a few days and do i need to rejet if i take the sparky out for a litte bit :yfz
 

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o and its like 30* out right now can i rejet by just moving my needle up and down cus i have no jets to work with there coming with my pipe
 

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Moving the needle down to the 6th clip will help a little but you are still gonna be lean at 3/4-WOT cause the fuel cant flow past the small stock main jet.
 
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