wrf450 2003 misfiring at 1/4 to 1/2 throttle

just brought a wrf450 2003 took it for its first ride on the road and it seems to be jerky and splatter at 1/4 to 1/2 throttle and is really noticeable by feel on the bike and the sounding of the bike. the misfire seems to go away as soon as I give it full throttle and takes of crazy fast, Ive removed the spark plug to see what the spark plug is like and it seems to be dry and looks like it might be running lean? could this cause this and what is the best way to go about it because I have no idea wat size jets are in it as I have just brought it? can the jets be adjusted and how? I tried taking it fot a run and then turning the choke on to see wat would happened and it just sounded like it got drowned with fuel. so yer any ideas

1/4 to 1/2 throttle is governed by the needle and clip position.

If it's rough I would guess too rich. Lean generally feels gutless.

Put the clip on the needle 1 or 2 positions closer to the top.

But to be sure you should remove carb and list all jet sizes and needle model and clip position and list them here.

Example -

Pilot (#48)

Main (#175)

Fuel screw (2 turns out)

Needle (OBDTM )

Clip (2nd from top)

There other reasons but start with the easy to fix stuff first.

sounds like normal to me

WR's not designed to cruise at constant speed - not enough flywheel weight

They do cough, splutter and generally mis-behave if you try to do this

The '03 and later WR's have a 'defective' ECU module; specifically the mapping curves.

It is made up of (3) 'sub maps', all dependent on rpm and throttle position.

1. Closed throttle, 2. partial throttle, 3. Wide open throttle.


At the sub-map 2 point (partial throttle) the ECU can't decide between sub-map 1 (closed throttle) and sub-map 2, so it toggles between them.  WOT (really before wot) goes to sub-map 3.


The quick fix is to unplug the TPS (at the harness, not on the carb). This will put the ECU in sub-map 3  all the time. A bit less throttle response at low rpms will occur.


The better fix is the PROPERLY calibrate your TPS, using the 9v battery method.  The method in the service manual is actually not correct IMHO.

For some, this solves the problem.  

For many, it just makes it different.

You must calibrate the closed throttle position with the slide dropped to the bottom (as in below idle)


The best fix is to put on a dynatek FS ignition system, and choose the stock (modified by dyna) Map #3, which has modified sub maps 1/2/3.

The Dyantek also allows you to calibrate the TPS in about 15 seconds, change the sub map turnover points, and advance your timing as you choose.

All stutter is removed in Map #3


I run Map #2, which I modified for performance only. The 2800 rpm stutter is still there, but I moved it down to 1/16 throttle with the adjustable maps, which is rarely ever used, so I only notice it on the street at certain times.

Edited by TheKoolAidMadeMeSick

Not sure what everyone above it talking about because I didn't get the impression you're talking about the slight stutter/hesitation constant throttle the WR does but a poor running bike at anything but full throttle.

Here's the deal:

You bought a 12 model year old bike with no idea the jetting it has in it and jetting is one of those things every goofball with a screwdriver thinks they can do. So what you need to do is start with a KNOWN baseline by completely cleaning the carb from top to bottom making sure all passages are clear. Read all the pinned threads related to "the bog" and jetting no matter how much you think you know. Then write down all jets and settings based on the chart Thommo listed above while you're in there. At that point compare what you have to what others have written about and either buy a JD jetting kit, or the individual correct jets for your bike again based on this forum.

At that point you should be good to go and only need minor tweaks to get it 100%. As well, make sure your valves are in spec, your air filter is clean, your timing is on and your cam chain isn't stretched past it's wear limit. Double check your exhaust pipe is on correct, all gaskets are in place and your silencer is in good shape packing wise. Do an oil change too along with a fresh tank of gas.

Now you're ready to go engine wise. Lots if info on body and frame stuff but before you go chasing all over be sure it's ready to run and be able yo know you're not chasing phantom problems.

Write back what you get, we're here to help.


Edited by miweber929

thanks for the replies it seems it has something to do with the tps as when I unplugged it and took it for a ride it seemed to fix it, and when I plugged it back in it would do the same thing again, is it bad for the bike to run it without tps untill I find a new tps??

thanks for the replies it seems it has something to do with the tps as when I unplugged it and took it for a ride it seemed to fix it, and when I plugged it back in it would do the same thing again, is it bad for the bike to run it without tps untill I find a new tps??


 Your TPS is not defective. Read my post above.

It has a fmf power core 4 exhaust, mj is 170, pj id 50, fuel screw 2 turns out, clip 2nd from top, the carb is a keihin fcr?? If that helps

Hi everyone I pull down the bike a couple of days ago cause 4th gear was missing a tooth, got 4th gear pinion and dog gears for 180$$$, during the pull down I found that the woodruff key in flywheel had been shorn off!! This would have caused the shuttering with the tps and the problems I have been having...

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