The joy of jetting.....

14 replies to this topic
  • yamageezer

Posted December 12, 2005 - 07:33 PM


Alright, I can't take it anymore :p I've been trying to jet my 05 WR450 for months now, and it's killin me smalls. Here's what I have going; I ride @ 4000-6000 ft 40-60 deg, 168 main, 45 pilot, zip-ty 1.5-2.5, ais removed, air box opened, YZ pipe, & JD kit blue #3. I have 1/4 to 1/2 throttle stumble, and a idle that has a mind of it's own when the engine is good and warmed up. No popping on decel :applause: I've read where 1/4 throttle stumble means too rich I have a black plug, black tail pipe, I'm burning up fuel, only 30 miles to switching to reserve. I've read where a fast idle when warm means I'm running lean. I'm at a loss at what to do. I've followed Indy's and JD's recommendations and I just can't figure it out. Can anyone please help. :ride: :p


Posted December 12, 2005 - 07:36 PM


Ask "Burned" in the jetting forum, The guys the bomb.

  • crooks420

Posted December 12, 2005 - 07:57 PM


Hey Yamageezer,

I also have an 05 WR450; the mods I have done are as follows:
Grey wire
UNI filter
PMB insert
AIS removal
Snorkel removed
Throttle screw
I added the JD kit and the Zip-ty fuel screw (I think at 2 turns). I went with a 168 main, and blue needle at 3rd clip. I just rode up at Bell Mtn. (off the 15 frwy), which I think is at about 2000-3000 feet. The bike runs great. Starts easily, and idles nicely. The power difference is awesome. I have not done anything else, but i am only planning on changing the main jet when I ride up in Big Bear next spring. I do notice barely a bog right off idle.... which is most likely the acelerator pump. I am not sure if or when I will mess with that.


  • rich1167

Posted December 12, 2005 - 08:05 PM


I don't know about the idle. But a different leak jet and AP timing adjustments would help the off idle bog.
Here are my settings. I rode this weekend and it boged 1 time when I was in to high of gear. But I agree you need to ask burned.
Ap adjusted 1 turn ccw
Elev: 4500 to 8000
30 to 55 OAT
168 main
48 pilot
0 leak
1 1/2 fuel screw
JD blue 5th pos.

  • Matty05

Posted December 12, 2005 - 09:23 PM


Nah... just put in JD red #5 and go to a 48 pilot if you have to.
Pilot circuit still affects the whole throttle range.

  • Dan_Lorenze

Posted December 13, 2005 - 06:58 AM


I think a 45 pilot is perfect for your elevation and temp. I would try a 165 main, an 04 WR needle with the zipty at 2 out.

  • yamageezer

Posted December 13, 2005 - 07:47 AM


Thanks guys, I went ahead and installed the red needle #5 yesterday. My next step is the 165 main, and if that doesn't work then I'll pull my hair out, oh wait, I don't have any hair, anyway, thank for the input, I did leave a message for Burned. Last question, is a hanging idle a sign of a lean pilot circuit or a rich one?

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

Posted December 13, 2005 - 11:05 AM


For you elevation I think your pj is too rich. For some reason there is a really popular myth to have an overly rich PJ to aid starting. My bike has what might be considered a lean PJ and MJ profile but it works perfectly from 5000 to 11,000 feet and starts right up.

I have a yzf which of course is gonna have different jetting, but everyones advice on my bike and the way it came jetted when I bought it had it overly rich throughout the range and I had the same symptoms. Even fouled plugs. I do a lot of trailriding and occasional enduro races, so keep that in mind.

And, only change one jet at a time. Dont' go and change out a MJ and a PJ in conjuction or you won't know the true nature of the changes.

Go check out the YZF jetting forum for some of my jetting hassle.

  • Matty05

Posted December 13, 2005 - 03:26 PM


Last question, is a hanging idle a sign of a lean pilot circuit or a rich one?

Adjust fuel screw out, more than 2 1/2 turns out, go bigger to 48.

  • clark4131

Posted December 13, 2005 - 06:06 PM


Pull your fuel screw and make sure you have the spring, steel washer and rubber o-ring. Also make sure the little pin at the end of the screw hasn't broken off inside your carb. Then check your Hot Start from lever to plunger. Make sure it isn't binding anywhere. Do the same for your throttle cables. I chased a hanging idle for 2 months until I found the problem and it was my Hot Start.

I'm at almost identical conditions, same elevation, but a little cooler, staying in the 40's. I'm running a 170 Main, 45 Pilot, 80 PAJ, JD Blue #4, 42 Leak, XXXXX-17-00 AP Diaphragm w/ Quickshot, 72 Starter and around 2 turns on the screw. I'm running great, zero bog or stumble. If I were you, I'd pull the carb, open it up and clean EVERYTHING. If you've been running rich, you likely have some crap in there. Pull all your jets and soak them in carb cleaner. Liberally spray the inside of the carb and then blow it out with some compressed air in the 60-80 PSI range. Blow out the jets and visually verify that they're not clogged. Verify your AP timing per the manual. Also check the rubber joint that connects the carb to the cylinder...mine was cracked and had a substantial air leak. Verify that your slide moves properly and that the slide plate is installed properly with the flat side down. Once that is all done, put it back together and retry. If it's still a no go, then I'd suggest checking your valves as a tight valve can mimic carb issues. While you're at all of this, put in a fresh spark plug too. It's cheap and can't hurt.

Beyond that, I don't know, but I'll bet if you follow the above instructions, you'll fix your problem. Good luck!...SC

  • yamageezer

Posted December 13, 2005 - 07:44 PM


Hey SC, I pulled the carb last week because I was only getting 15mpg, I was thinking I had a float problem so I changed my float from 8mm to 9mm, since I was into it I went ahead and cleaned out every jet and blew it out with air, so I know that end is good. I was thinking about the valves the other day, I haven't had them checked yet, I was going to wait, I only have about 470 mi. on the bike and I wanted to check them at 600 mi. Maybe I'll do it sooner if the needle, and fuel screw change I made doesn't work. Thanks for your help. :applause: :ride:

  • Moondogger

Posted December 13, 2005 - 09:18 PM


I feel your pain. I went through all the problems with the stock carb. One day I came back from a ride and saw that my Zip-Ty fuel screw had fallen out (which I found out later here that it's happened to other people as well).

That was the last straw.

I installed an Edelbrock carb and now I don't have to worry!

  • yamageezer

Posted December 14, 2005 - 07:58 AM


I feel your pain. I went through all the problems with the stock carb. One day I came back from a ride and saw that my Zip-Ty fuel screw had fallen out (which I found out later here that it's happened to other people as well).

That was the last straw.

[COLOR=Red]I installed an Edelbrock carb and now I don't have to worry!


Edelbrock, where and how much?


Posted December 14, 2005 - 08:21 AM


One more stupid idea. If you've had the slide out of the carb make sure the plate that sits at the engine side of the slide is oriented correctly. It is very easy to put it in upside down. It will run that way but causes all kinds of idle and partial throttle problems. Don't ask me how I know! :applause:

  • yamageezer

Posted December 14, 2005 - 09:42 AM


Thanks, No I didn't take the slide out but, thats funny, it sounds like allot of guys have done that so I will pay special attention to that when I do remove the slide. Ya know it's also funny how such a simple mistake :bonk: like that can 1. make the bike run bad and 2. how it will drive you :applause: until you figure it out. Trust me I've done my share :cry:


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.