Weird Jetting problem

Hi, i have a wr450 03 model, all free mods + aftermarket wileyco exhaust.

i had the standard needle and main jet was 160 and 48 pilot and it didnt run too bad.

I bought a JD jetting kit and installed the 168 main jet and red needle on clip 5.

It ran alot smoother at midrange - it used to have a bit of a rough misfire or something. BUT when the revs get to top end it would burble and struggle like it was way too rich.

So i changed the main jet to 165 and it got better but it still struggled a bit.

Now im back to 160 and its almost back to normal i think.

the tempreture is only about 15 degrees celcius and im about 250 metres above sea level.

The bike felt like it had more power with the larger jets and everyone else runs a 168 with no problems.

what could be causing the bike to be soo rich up at top revs.

any suggestions to what i should do?

I also installed the rubber o-ring on the fuel pump acctuator and now it has more punch from that mod.

i dont want to stuff around forever with my jetting so i thought i ask for some opinions.

by the way my air filter is clean and not overoiled and my airbox is opened up.

Thanks for the help in advance.

Any ideas anyone?

When i had the 168 in, it pulled alot harder to top end but then just started spluttering at about 3/4 top revs.

by indys chart i should be running a 170 main.

i want to get it running right because with the 160 jet it dosent pull hard enough up top, and i dont think i have ever hit the rev limiter on the bike - i think it just splutters up top when i originally thought that was the rev limiter.

Please help Anyone.

You said you had done all of the free mods, but I have to ask the dumb question. Did you remove/replace the WR throttle stop with the YZ one?

I am no jetting guru, maybe you should PM one of them like Indy or Grayracer. Sorry I can't be much help.


hey, at least its a reply, i was beggining to think no one likes me.

Anyway, i have removed the snorkel and cut out the two holes on the side of the air box.

Throttle stop has been replaced with YZ.

exhaust has been replaced with wileyco muffler.

grey wire cut.

i think thats all of the free mods.

I seem to be the only one with this problem, there is nothing similar to my problem when i search for it, except for earlier WR's with a removable main air jet, but the 450's has a fixed 200 MAJ.

just keep throwing your theorys my way, i will be willing to try any suggestions.

One thing I would try would be to put your 168 back in there and try leaning out the pilot a little bit to see if that makes that changes you are looking for. Jetting is funny, you really don't know what you are going to need to set it at until you try a few different tunings and find the one you like the best. You will also want to start tuning your fuel screw when you start changing pilots. Hope this helps, like I said, for more specific help you could PM a few of the guys who have been around these machines forever.


Ok update on whats happening.

Today i put the 168 back in and tried it with my original needle on clip 4.

Still the same but dosent have as much power - i think the other needle gave it a bit of a power boost - im starting to think that the 160 is just perfect with my bike for some reason. Although i then tried running it with the air box cover removed and i think it reved a tiny bit higher before sputtering.

Tommorow i am going to give the air filter a really good clean and go very lightly on the oil and see how that goes, then im going to try the blue needle on clip 3 and see if thats better than the red needle.

If the air filter dosent help then im just going to have to stick with the 160 main and play around with the needle a bit to get some more kick out of it.

If anyone has any ideas please SHOOT!

Sounds like you are getting into it pretty well. Don't forget about the fuel screw, if it is not adjusted properly for each jetting then it can cause you to pull your hair out. Good luck,


yeah the fuel screws set to 1 turn out with the 48 pilot, thats the point with the highest idle and quickly drops back to idle after a quick blip.

i tried adjusting it with the different jet sizes but it liked 1 turn out with all the jets.

All I can tell you now is good luck and find the settings that work best with your machine. If you don't have it right, it will let you know. Have fun and good luck.


Cheers Mate

stock main and turn the air screw out 2 turns with needle in position 4.

48 pilot

works for me

Good luck

is the 160 stock on your bike?

Thanks for the input.

165 is stock on the WR426.

i cleaned my airfilter on friday and i soaked up as much oil out of the filter with paper towel as i could but coudnt test the bike as it was pissing down rain.

ill do some tests on saturday and see how she goes, ill keep you all up to date.

Tried the 168 + 165 with a clean air filter and both were too rich, went with the 160.

tried the blue needle on clip 3 but i think that was a bit too rich down low so i went with the red needle on clip 5. there was a noticible power increase in mid range when changing my standard needle for red #5.

So thats what i came up with, with my testing.

I have found the ACV to make a big difference on the pilot circuit. For example I disabled the ACV and my 06 WR450 runs best with a 40 pilot 1-1/2 turn out.......Trust your instinct and have fun trying different sounds like your on the right track to me......just my opinion.

thanks mate, i just find it hard to beleive that there is such a major difference between bikes jetting, arnt all the engines created equal?

Hi mate,I have been jetting a mates '03 wr 450 and we did all free mods,yz mufffler,jd jetting,acv blocked and i found 48 pilot 165main jd red on 4th clip.on wr timing and 98 octane worked fine and when i put in the yz cam and did the tappets,the jetting is still ok. Have you drained the fuel tank and carby float bowl?:applause:

the fuel was fresh BP ultimate ans the float bowl got drained everytime i made jetting changes, i might change the needle clip to #4 and see how it goes, although i couldnt really be stuffed until i have a few rides, so ill get back to yas in a couple of weeks and tell the results.

If you are running racing fuel then that could account for the differences you are seeing when comparing your jetting to others. Just a thought.


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