What to do?

9 replies to this topic
  • Pete..

Posted March 27, 2002 - 04:36 PM


Ok im sure my WR426 is running lean but i dont want to go through all the mucking around with re jeting (Just because thats one thing i know nothing about at all)I have removed the airbox lid and have a FMF exhaust So should i just back out the air fule screw or would it be better to move the clip position? It is an australian modle and nothing hase been ajusted at all from factory Please help what do i do i really need help

Yours sincearly Pete..
Wellington N.S.W Australia

[ March 27, 2002: Message edited by: Pete.. ]

  • Pete..

Posted March 27, 2002 - 05:32 PM


me again i just pulled the plug out of the WR and it is fairly black? but im sure that the bike is runing lean but the plug says its rich so this just dosent make sence to me And i also checked the air fuce it is at 2 turnes out as it was when i got the bike new anyone?

[ March 27, 2002: Message edited by: Pete.. ]

  • ratbiker

Posted March 27, 2002 - 06:07 PM


cannot help you but a chap named taffey is working on my jetting.I have an 02 wr426 yz timed and same stuff as you i have a post up.http://www.thumperta...f=3&t=007494.he says he will look ai mine and let me know if you put a reply in there asking him for help i am sure he will give it a go good luck.oh ya mine is a canadian version so it is the same as yours so maybe you could use the info he gives me and give that a go! :)

  • Mark_Cantrell

Posted March 28, 2002 - 03:51 AM


A bike can be lean at some throttle positions and rich at others. Where do you have lean symptoms?

If a lean pilot/fuel screw, the idle will hang above idle for up to 20 seconds before finally dropping to idle. If pilot jet/fuel screw rich, the idle will be rough and inconsistent. When just right the idle will come down to idle almost immediately and stay at the same RPM. It will also require choke when not warmed up to start and for 30s to a minute depending on temperature.
For lean turn out fuel screw and if out of adjustment (too many turns) try larger pilot jet. For rich turn in fuel screw and if out of adjustment (turned almost all the way in) try a smaller pilot jet.

At higher throttle positions lean will seem very snappy and feel good (until way too lean) but will snap and pop. Rich will lower acceleration and give a bboooowaaaahhhh sound. At less than 1/2 throttle try adjusting needle (if lean lower the clip position which raises the needle and if rich raise the clip position to lower the needle). At 1/2 or more throttle position, change the main (if lean, go larger and if rich go smaller).

If you know nothing about jets, the top of the carb comes off with two 3mm allen screws. The top of carb lifts off and in the throttle slide (the thing you can see moving up and down when you twist the throttle) is a 4mm allen screw. Remove that allen screw and lift out the stubby screw, the spring and the collar that is under it. The needle is underneath that. Lift it out with tweezers (or by turning the bike over and bouncing it, JK). The clip can be moved with needle nose pliers, just DON'T LOSE it. This can be done with the carb attached but with the tank removed.

The main jet and the pilot can be changed simply by turning off the fuel, removing the 17mm bolt at the bottom of the carb (about 1/2 cup of fuel will spill out) and using a small (5mm?) socket on the main or a screw driver on the pilot. If the main is over 1/2 inch long, the needle jet came off also. Just replace the main on the end of it and replace both together.

This is just the rawest basics. There is also needle shapes and sizes, air jets, and accelerator pumps. Only Taffy and JD and Rich in Orlando (is Rich is real name or his carb condition?) can help with those. In fact, you may very well have a lean running carb with an overagressive accelerator pump to give the lean/rich symptoms. If so, the BK mod might fix it.

Reply and tell us what symptoms and when make you think it's lean.



Posted March 28, 2002 - 05:24 AM


Rich is now a Jetting God???

Someone roll out the red carpet......

Bonzai :)

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

Posted March 28, 2002 - 06:39 AM


Nice jettting intro there, Mark.

Truth is, all the jetting god posts in the world won't help you until you get comfortable swapping out jets and such.

Anybody remember when you still had to tune in a TV channel by turning the knob? Then you had the fine tune knob to bring in the best signal. The best anyone can do for you over the internet is send you a "TV guide" that tells you what channel to turn to. After that it is up to you to adjust the "fine tune" to get the picture to come in nice and clear.

With a basic understanding of how the jetting components interact and overlap (a lot of this info is in your manual), you just keep turning that TV dial back and forth and watch what happens to the picture. You'll start to see for yourself what makes the picture clearer and what makes it fuzzier.

  • racemile

Posted March 28, 2002 - 01:26 PM



After running through the manual on my 02WR 426, I found a chart/diagram that explained what part of throttle application, was controlled by what jets or jet combos. While I didnt study it and have only changed MJ to 158 (done at bike purchase) It gave me a lot of confidence in regard to my ability to diagnose which jets really need the attention/change. Maybe someone else out there has seen the same chart and can tell us if its effective or not. In either case it graphically demonstrated the relationship between pilot screw, jets, clips and clip positions. Good luck :)


Posted March 28, 2002 - 03:30 PM


I have been jetting Carb's for years (other than the FCR's) this thing drove me nut's until I took the time to understand how it works. Order the Pilot Air Screw pn# 021-230 and Spring pn# 021-235, about 4 main jets richer and 4 leaner than stock, pn#s 019-131,019-132,019-133,019-150,019-134,019-151,019-135,019-152 (155 - 172). Slow Jets pn#s 019-005, 019-006, 019-007, 019-008, 019-009, 019-010, 019-011 (35 - 50). Main Air Jets pn#s 019-202,019-206, 019-210, 019-214, (160, 170,180,190). This is way too many parts, but you will have enough parts to attain whatever jetting you require without the pain of reordering and waiting for more parts. all of these parts plus shipping cost me about 70 bucks. All of these are sudco Part #s the phone # is 1-800-998-3529. Do a search on jetting Q's and yes, the back of the factory manual is very helpful also. Set your Main Jet first then go from there. If you still don't get results just ask. I don't know what your stock needle is, Mine is a DRR, I raised the clip One notch.

Good Luck

  • Pete..

Posted March 29, 2002 - 10:46 PM


Ok thanks for all the info but i have now turned the air fule out to 2 and a half turnes From 2 (After i found the screw stupid workshop manuals can never find anything in them) Is it turned to far out? it seems so mutch better when i give it a rev it will go straight back to idle now and the whole bike seems to pull as hard but is a lot smother all through the rev range
So i think it may do now but can i make it any better now thats the question?

  • Pete..

Posted March 31, 2002 - 11:19 PM


Took th WR for anouther ride today and rode for a while and went to pull a wheel stand up the tar road got to 5th gear reving fairly well it started to jump like the chain was jumping any way i dun it again but the same thing happened
so i desided to take it fot a run along the road and at about 145kmh it started to do it again and i know its not the rev limeter because it dosent cut in till about 165kmh
so has anyone any idears?it runs fine other wise
And it only dus it in 5th gear i can hit the rev limeter in all the other gears and nothing

Yours sincearly Pete..


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