Throttle position sensor

Hey guys. I ride a 2001 WR426 and Ive heard from various threads that the TPS is what makes the bike miss at steady throttle and so Ive never been too worried about it. I was just wondering to what extent this should be happening.

Im currently getting the bike ready for rego and gave it a run on the road the other day. At about 100 km/h it was spluttering so badly at steady throttle that I had to hang on for dear life.

Is this normal and if so is there anything I can do to minimise it?

The odds that the TPS is in any way connected to the 'miss' is minimal, however to check it out, unplug the TPS and ride the motorcycle to see if the engine runs any differently.

My 02 with sputter now and then at constant throttle but nothing like what you are describing. It’s more like a hiccup or like its heart skips a beat. I tried running with it disconnected and the hiccup goes away but it doesn’t seem to be a responsive off road with it disconnected.

Will do. What else would be causing it to run the way it does? It definately feels electrical, and the bike runs fine under heavy throttle, its just when you hold it steady starting around the mid rpm range.

...or it could be a simple jetting issue. At a steady speed, were you were at ~1/4 throttle? My '03 would skip, although not as badly as you describe until I finally got the pilot circuit dialed in. This would be an easy thing to check before chasing electrical gremlins.

WR CDI. Much effort has been done to verify it is not jetting. So far, the only solution has been a Vortex CDI and even then, only one ot two of the supplied maps seem to make it go away. I thought I had gotten rid of it on my WR, but a recent ride showed I still had it. Bike runs perfect on the gas. Mid throttle and up (from about 6,000 to 9,000 rpm), steady state riding, the miss is there. Crack the throttle and the miss magically goes away.

Read the Manual on setting the TPS. You must set the system voltage with the system contected (circut complete) by back probing the TPS connector. The Manual gives a voltage range for setting the TPS i believe the range is between .58 and .78 volts .

Set your idle as good as you can. Then adjust the TPS voltage to about .75 volts or on the high side of the voltage range without going over the .78 volts.

You need to move the TPS after loosening the tamper proof torx screws holding the TPS to the carb. Yes you will need to get the right tool for the job.

This adjustment will not completely eliminate the "Stutter". however this adjustment combined with proper jetting will significantlly reduce the effect to a manageable level.

after all this was done I raised the needle one slot. however you should test drive after the tps adjustment to see if that is what you need. Now the only time I feel the "Stutter" is on the pavemment at 1/4 throttle cruise.

Good luck.

For 03 and newer WR450's the dynatek CDI is a much better way to go than the vortex.....much cheaper too. See link:

http://www.thumpertalk.com/forum/showthread.php?t=697660&highlight=

According to dynatek data the TPS simply tells the CDI to output spark advance according to either one of two map curves....either a low throttle output or a high throttle output (more advance). This is why there is less stutter with TPS disconnected because there is less advance at "high" throttle. For some reason the WR450 has MORE advance at WOT rather than less which is backward from most internal combustion engines.

Thanks guys. Im new to this bike and to electronics in general, so what is the actual function of theTPS and what would happen if it were disconnected. Sounds like this might be a job for my dealer which is fortunate since I have to drop it in for rego anyway

Many folks claim that their bikes run better with the TPS disconnected. It's easy to do....just unplug it, and it does absolutely no harm. You don't need a dealer to do this.

The Throttle Position Sensor (TPS) functions by adding small amounts of advance to the built in (factory default) advance curve during low rpm and part throttle operation much like the vacuum advance in cars.

Thanks guys. Im new to this bike and to electronics in general, so what is the actual function of theTPS and what would happen if it were disconnected. Sounds like this might be a job for my dealer which is fortunate since I have to drop it in for rego anyway

TPS is a primitive way of advancing or retarding advance.

WR curve shows advance at WOT:

WR450.jpg

RMZ400 curve shows less advance at WOT:

RMZ400.jpg

I see. Well next time Im home Ill disconnect it and see if it makes a difference. Thanks for the help

TPS is a primitive way of advancing or retarding advance.

WR curve shows advance at WOT:

WR450.jpg

RMZ400 curve shows less advance at WOT:

RMZ400.jpg

These advance curves provided for the WR and the RMZ are very interesting. The curves for the RMZ make sense to me, i.e. less overall advance at WOT. However on the other hand, the WR advance curves do not make sense due to the fact that there is more total advance at WOT and less advance at part throttle. It appears to me that the advance curves for the WR are indeed backwards as the advance requirements should be for more advance at part throttle for economy and less advance at WOT to provide the most HP and suppress detonation at the same time.

What is the source of these advance curves?

Chas M, I agree but that is how a Wr450 is......the curves are from Dynatek......in order to view them you have to download their curvemaker program and install it on your computer.

spluttering so badly at steady throttle that I had to hang on for dear life.

QUOTE]

if you're serious that the perceived engine misfiring caused the bike to react so radically that you had to hang on much tighter, my first impulse is that no level of misfiring could be the cause of that radical of a response.

my first thoughts are that the engine could be trying to seize up. possibly a wheel bearing getting hot and trying to seize? i'd bet on the engine at the moment. if that is the problem, you'd best be ready to grab the clutch if she does seize. a rear wheel slide at that speed will put you on the ground in a heartbeat.

i recently inherited an 01 wr426. it was surging at very low speeds. the faq section indicated this was the normal behavior of the tps and recommended disconnecting it. i did and the problem disappeared. i did not read anything about the tps causing problems at higher speeds.

Ok I might have been exaggerating a bit, but it was stuttering quite noticeably, probably no more than in does at lower speeds it just felt worse because I was going quicker I guess. The first Im going to do is disconnect the TPS and see what kind of difference it makes

ok. we're dirtbikers. we all embellish at times.

if it doesn't clear up with the tps, and you test in a location where you can coast off the road and work on it, i think i'd pull in the clutch, hit the kill button, coast to a stop, pull the tank and take a look at the plug. or just go on size larger on the main and retest. i'm now thinking possible a little lean at the very top. it's a pain to check the plug on the trail/road.

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