NEW Jetting Stuff

19 replies to this topic
  • doc4523

Posted June 06, 2003 - 08:43 PM


:cheers:Today, 6-6-2003, I was at my local Yamaha dealer in sac CA to buy a MJ#162 and a PJ#50. When I was talking to the mechanic about rejetting, he said the factory released a FREE Carb modification for the 2003 wr450f. Apparently they take out the LEAK JET, "see page 4-10 and 4-11 in Yamaha manual," and solder the hole closed on the jet then redrill it with a .013 drill, and I think he said they move the needle jet clip up one grove from the #4 position but don't quote me on this one. The mechanic said this factory fix fixes the FLAT spot inherent in the wr450 response. He also said this is all done without changing the other jets from the factory settings. I just got my wr450 last week and I was very unhappy with the initial performance. The header pipe would glow red while stopped and the backfiring while going down hill was annoying, and the was very hot which is not conducive to riding in CA during the summer i.e. FIRE hazard. Today I replaced the PJ and MJ with a 50 and 162. I also installed a Powernow carb insert; a Promoto exhaust silencer and a zip tie fuel mix screw. I have not yet cut the gray wire or modified the throttle stop. Aww all done, now for the test ride. "Wow" my right calf is not on fire any more, the throttle is not twitchy, and "wow" the header pipe is not red hot. I live in for foothills of CA around 2500 feet for a base line. Next week I am going to get the fix done to my bike and ill report on the findings.

  • Indy_WR450

Posted June 06, 2003 - 08:51 PM


You are on the best forum to mod out your WR. There is a lot of great experience from our TT members. Thanks for posting your experience with your bike. Cut the gray wire immediately. :)

  • Hick

Posted June 07, 2003 - 04:53 PM


Apparently they take out the LEAK JET, "see page 4-10 and 4-11 in Yamaha manual," and solder the hole closed on the jet then redrill it with a .013 drill

Why don't they just use a smaller leak jet?

  • doc4523

Posted June 07, 2003 - 07:16 PM


I asked the same thing when I was there and he said the factory did not have any in stock. I think the factory is cost saving by just modifying the existing part. The mech said it take about 10 minutes to do the mod.

  • wrkaholic

Posted June 08, 2003 - 05:31 AM


You will keep being disappinted with your WR until you remove the throttle stop & cut the grey wire. Then, hold on.

  • doc4523

Posted June 08, 2003 - 08:58 AM


Today I cut the gray wire but I have not cut the throttle stop yet "only 45 mile total on the bike." What is the size of the throttle stop after cutting it down? and yes is do notice a differnce in the responce.

Has any one had the leak jet mod done???????? And if so whats your story....

  • Hick

Posted June 08, 2003 - 11:41 AM


I asked the same thing when I was there and he said the factory did not have any in stock.

I wonder if a leak jet off a 250f will fit, or if Sudco or Carb Parts Warehouse has this part?

  • sabin

Posted June 08, 2003 - 07:29 PM


Do we have this leak jet on 2002 426?

  • jimmyboy1

Posted June 09, 2003 - 06:59 AM


INDY,I have a 98 WR400 and just changed it to the YZ timing. What does the gray wire do! Does the performace change.



  • RPS

Posted June 09, 2003 - 07:55 AM


I would definately recomend changing to a smaller leak jet verses what you have described in your original post. Stock they come with a #80 leak jet and I would recomend going to a #40 leak jet. It is not listed on the WR450 Microfish buy is available from Yamaha. I have the part# at work and will post it when I go to work tommorow.


Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • Lowedog

Posted June 09, 2003 - 02:21 PM


Wanted to keep this towards the top to see if any one has any more info on it. My book shows the standard leak jet as a #70. Does any one know what the YZ 450 has for a leak jet? I couldn't find it listed on the online diagram.


  • Hick

Posted June 09, 2003 - 06:05 PM


Do we have this leak jet on 2002 426?


  • Lowedog

Posted June 10, 2003 - 02:37 AM


I don't think the YZ 450 has a leak jet either. What's the purpose of the leak jet?


  • The_Missile

Posted June 10, 2003 - 03:08 AM


If the leak jet is the same as the ACV then I may be right in thinking there is no leak jet on the YZ. In tha past the WR carbs were different than their YZ cousins due to EPA emmissions standards. On past WR's 98-99 you could literally rip all that crap off (de-octopuss) and with a small amount of rejetting have a much simpler and stable carb set up. There was a similar mod on the 2000+models which involved blocking a little hole with a rubber pad which essentially did the same thing.
Then again I may be barking up the wrong tree...its been a while since I last logged on....

  • Hick

Posted June 10, 2003 - 06:07 AM


I don't think the YZ 450 has a leak jet either. What's the purpose of the leak jet?


The leak jet meters the amount of fuel delivered by the accelerator pump. I can't find one on the YZ 450 fiche, and I can't find a WR 450 fiche at all.

In the past, aside from actual jets installed, the WR/YZ carbs have been identical internally, so I'm surprised this no longer appears to be the case.

  • Millertime

Posted June 10, 2003 - 08:46 AM


you can install a yz screw or just cut off 11mm from your screw, same diff. This will make a huge difference. Enjoy.

  • Lowedog

Posted June 10, 2003 - 12:12 PM


I talked to the service manager at the local Yamaha dealership today about this. He claims that he is constantly checking online for service bullitins and has not heard of this one. He also doesn't think Yamaha would authorize a fix like this. That they would replace the jets and not solder them closed and re-drill them. But he also didn't know what a leak jet is either so take that for what it's worth.


  • doc4523

Posted June 10, 2003 - 07:15 PM


Ok I’m back and I just got done with another re-jet of my 450. I have not had time to get the leak jet mod done but I did re-jet because my sparkplug rim was black “leaning it up a little.” While, re-jetting I pull out all of the other jets to get there number, and I took picks. So here we go.
Main jet=160 "factory was 155"
Pilot jet=48 "factory was 45"
Starter jet=68 "factory"
Pilot air jet=70 "factory"
Leak jet=70 "factory"
Jet needle= #4 position “factory”

Bike mods
Factory pipe with the promoto insert “96db”
Adjustable fuel screw TIE “2.5 turns out”
Power Now carb insert
Gray wire mod
Throttle stop STILL Factory “I’ll get to it!”
Riding around 2500 ft

Yes, its true the YZ does NOT have a Leak Jet.
Yamaha web site has fish tape on all the bikes except the WR ??????? I have not found any site that has it. I think Yamaha has not published it yet.

To the picks

Thanks Hick, Lowedog and Millertime for the factual information.

  • Indy_WR450

Posted June 10, 2003 - 10:04 PM


I think I heard someone post that Yamaha racing recommends a #40 leak jet. Can anyone remember this post?

  • 450roost

Posted June 11, 2003 - 10:11 AM


Has these jet settings worked well? What is your elevation and temp? :)


Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.