Med/high speed hiccup on 04' WR450

The TPS on our bikes are about the same as passenger cars. I suspect ours is like the earlier design (single pole, double throw switch (SPDT) and it operates where there is one common input and 2 other contacts, one set is closed at idle, the other set is closed at wide open throttle, and both are open anywhere in between. I doubt we have the high tech linear types by the way the timing is jumping.

AFAIK, the TPS is a variable resistor...just reading the adjustment procedure tells me're adjusting the TPS voltage. It's easy to check, just unplug the tps, connect an ohmmeter and twist the throttle...

Ok, so the TPS is a linear pot-resistor, but this means that the timing change is a step function (not linear). And it just so happens that the 'black box' cannot decide what timming curve to use when I/we ride at partial throttle with a light load. Sort of like going up a slight hill with an automatic trans car, and the tranny starts shifting in and out of OD.

So.... I guess the best and only solution is to RIDE FASTER! Or unplug the TPS wire, depending on what type of riding you'd be doing.

Im really glad to know that we have a lot of smart and helpful people in the Yamaha forum.

Thanks everyone!

I never had this problem with my 99 wr400,I am going to see if my 99 CDI unit will fit my 03 wr450,it bugs me that the engine misses at a steady throttle postion,I will also investigate fitting the 99 tps,I have had extensive jetting and needle changes to make this problem go and have come to the conclusion that it is ignition related,weird thing,I have installed a torque valve in the headpipe and after 2 rides the problem seems to have disappeared at steady throttle,but I now have a miss at roll on down low,I will post results if 99 electrics fix problem.

The cdi unit and tps from your 99 wont fit the 450. Here is what James Dean wrote about this problem under another thread:

I've had many, many jetting dialogues with WR owners on the light throttle steady speed stutter problem. It's a Yamaha issue and most noticeable on WR400-450's and WR250's.

---Disconnecting the TPS is the only consistent answer. Disconnecting the ACV and different jetting doesn't normally solve the issue. The condition seems worst on flat, paved road at a steady speed of 30-50mph.

The condition should not be confused with overly rich jetting causing a sputter and miss, or lean jetting causing a lag or bog. Work to refine the jetting carefully and the condition will only be found at a steady mid-throttle cruise.


After much head scratching and rewiring including fitting my 99 loom and cdi as well as the carb I now have a wr450 that does not pop at steady throttle and does not backfire on decel,however this was a real pain to switch over and a lot of stuff does not work now without adding more wiring and my 99 is denuded of wiring(no way I will swap 450 loom and cdi etc),I will be switching back this weekend and will just make a TPS on/off switch for highway riding,it is NOT the TPS fault,just it's input values to the cdi are to sensitive(read cdi is the real problem) does anyone know if an aftermarket cdi addresses this problem,WOLF,VORTEX etc?

I have/ had the same studder problem on my WR450 05 when cruising constantly. After lots of testing with JD Kit and jetting I went back to stock settings with the Yam original needle OBDUS. Now the bike runs rougher on accel, has a little Bog on quick changing from idle to full as with the JD needles, BUT the studder has nearly gone. There is only a very small studder when cruising on higher speed (about 60mph)

So I think there must be a solution whith jetting without disabling the TPS.

But additionnaly I also think ther is a big difference on the Euopean and US WRs ( grey wire does no affect, jetting seems to be leaner?)

Hope one fine day the jetting will be perfect or Yam will switch to injection :-)

i think you should always rejet from the factory based on your conditions

jd jetting is pretty much getting close to spot on

the tps is good for the dirt, but will cause the stutter at constant rpm in 5th

by the way i have a 99 wrf, i have the stutter, so its not the CDI, the only other thing that may differ in the wiring harness is a short, which would prob cause the bike to run bad or not at all, and the regulator is different, i think it was the 426s that got the upgraded regulator/rectifier

the wr400 is only regulated NOT rectified, the whole system runs on AC

...the studder has nearly gone. There is only a very small studder when cruising on higher speed (about 60mph)

This is the usual result after many attempts with rejetting. The steady speed, light throttle stutter can be reduced, but not eliminated by adjusting the carburetor. The same annoying symptoms were on my '00 WR400 and '03 WR250, but I didn't ride them on roads enough to care about it.


....I didn't ride them on roads enough to care about it

I am normaly not riding like this, but I will start to a desert rallye in a few weeks and there will be some connecting stages onroad :banghead:

Do you have any ideas how to jet with jd kit that comes nearest to Yamahas stock jetting. I noticed a smoother accel with JD needle that I would get again :banghead:


The Red marked needle in the 3rd or 4th clip position from top with a #165 main jet should be close to the stock needle at the throttle range where the condition is worst. --I mention the main jet because it also has a small effect at low and mid-throttle too.


Hi, Having same problem on my 05wr450F, i have baha kit installed, ride as supermoto and trails.

but mid to hi rpm it starts to bog but it goes away if i nail the throttle, i have a jet kit and adjustble needle jet. was wondering because this bike sat for a year in a gurage, b4 i take the carb out i want to see if C-foam will cure it.

any help would be great.

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