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

I would like to ask one quick question before I do this!
As of right now I just have my baffle out with the stock jetting, if I take the airbox lid off and rejet to your specs will I be able to tell a difference in power? Also since I am taking the airbox lid off it would be a good idea to buy and aftermarket airfilter kit right? Thanks! :tup:

Oh and sorry to be a pain, but I just read on a site where I am ordering my nerfs from. They sell pilot jets and main jets for different atvs. When I rejet does that mean that I have to buy all new jets? Sorry i am dumb with carby work. :nod:

You will be able to tell a HUGE difference when you pull the airbox lid off and re-jet. You are dumping a lot more fuel and air into the engine so it pulls WAY harder. It is a good idea to go to a higher quality air filter as soon as you can afford it. The stock one is fine but a good K&N or TwinAir filter is 100 times better than stock. Yes you will need to buy new jets in order to re-jet. www.jdjetting.com or go to your local yamaha dealer and buy a GYTR jet kit for the YFZ450. They are both in the 60 dollar neighborhood but you are purchasing something that will help your quad work better for years to come.
Isaac

Alright then, thanks. And as for the gytr kit that will be in about the $120 neighborhood, I live in Australia! But I have the money right now so I will just order my nerfs and the gytr kit all at the same time. :tup:

So is the 180 main hmf recommended too big?? I have a 180 main and 45 pilot right now, it seems to run alright but there's a little stumble off of idle (which I thought the pilot would fix). Also, I am shooting fire out of my pipe, is this caused from a rich condition or simply because i don't have a spark arrestor? Thanks for the help in advance

backfires are because of either too much air or too much fuel. Mine throws 4 foot flames when it is cold. the 180 that HMF recommends is not wrong but it will work if you dont want to mess with anything else. If you take the manufacturers recommendations you will be very close because different tuners jet differently. The jetting specs that I gave are very generic and work well for the Baldwin, HMF, Sparks GYTR pipes that are out there now. I talked to TC today and his pipe requires WAY different jetting.
Isaac

sounds about right to me. Do you have any hiccuping or hesitation in the power? Try warming the quad up and then slowly increasing throttle to about half throttle and then blipping it wide-open for just a sec. Did you notice any roughness in there? Where was it at in the throttle travel? All of these things will affect the jetting. Try and see what it does with the jetting you mentioned.
Isaac

Please help!

I've got a YFZ with fmf titanium 4, power bomb & YZ cam im getting a bit of hesitation from idle example if im at dle and open to full throttle it kinda shuts of the n sometimes pics up. what jets should i be useing and can I use the YZ dirtbike jets?

my guess was 168 mains 45 pilot and clip pos 5-6 running with lid on! as said above but just wont to be sure as it is an fmf pipe

You can use any jets that are for the Keihin FCR carb. Also the off idle hesitation is caused by an off setting in the mixture screw. I altered the setting on mine and was able to get rid of the hesitation. Try 2.5 turns out on the mixture screw and see if that solves your problem if that doesnt work keep messing with it until it runs to your satisfaction.
Isaac

thanks for the advice but to be sure i play with the right screw where is it

forget he last post i found it :hey: my hesitation hasn't improved and have noticed it idling and very low revs are a litle rougher but my deacceleration popping has stoped and it kinda seems more punchy :tup: the pilot thats in is a 42 so should i try a 45

yes you need to go to a 45 pilot. That will also help the hesitation off idle. The mixture screw is really a valuable tool when it comes to adjusting the first 1/8th of the throttle travel.

yeh i really does help, I've also found that these carbs are fairley easy to work on as each day goes by i'm finding more and more good things about the yfz 450 :tup: I'll get the 45 pilot can i ride until they come in i don't think my dealer will have them for a few days friday is when i should get them

I got the TC pipe yesterday and his recommendations are whacked. Stock main and pilot, clip in 3rd position mixture 2 1/2 turns qith lid on stock cam timing. Well my but cause I got a 5 inch flame threatening my back number plate. I'm gonna try the 168 and 45 tonite and I will post my results, oh and there is no way that lid is staying on either :hey:

I just added a picture of the main, pilot, and starter jets in the original post above since some are confused about which is what.

How do you know if you're jetted too rich on the main jet? Can you put a tachomoter on the YFZ to see if jet changes affect the wide open throttle RPM?

BTW- do inductive tachometers work onthis engine since the secondary coil is connected right to the spark plug?

RG, I would take Tom's advice. He knows what he is doing. I talked him about a week ago about getting one of his pipes and he told me the same thing. Of course he also thinks the cam mod is BS so I dont really know what to thing of that.
RPYFZ,
You can tell if you are too rich on the main if you cant get to the rev limiter. But as a general rule the richest you would ever need to get is a 170 main. I know that HMF calls for a 180 but that is if you dont change anything else.
Isaac

Edgerat, are you saying I should hit the RPM limiter in 5th gear? Thanks

yes you should. I do. I am running a 168 main at sea level and I can hit it no problem with my Sparks pipe and YZ exhuast cam.
isaac