Wr250 throttle position sensor

[rhinoracin]

I have a 2004 WR250. I had to replace the throttle position sensor because the readings were out of the specified range and the bike wasnt running that great with it not working properly. I already posted this on the yz/wr250 forum, but i though i should ask here as well.

Here is what i just posted on a thread in the 250f forum:

I just replaced the TPS and followed the manual's instructions on everything. I set the idle, checked the output voltage and rotated the TPS until i got in the specified range, and checked the input voltage and that was good. For just replacing the sensor, this is all the manual said to do.

I went a little beyond that and wanted to make sure all the readings i did before were in the specified range. Im not even sure if i needed to do this. well the same thing happened...the first 2 readings were good, but the last reading (full throttle) wasnt. I was doing everything right with my volt meter. I even checked my 07 WR250 to see if the meter was working right, and i got all good readings on that bike, so i guess the meter is fine. and the TPS really is good on that bike.

So on my 04 wr250, i tried to get all good readings by rotating the TPS and that didnt work. The only one that's always off is the full throttle reading. The closest i could get that to the 4-6 range was about 3.78. but with that reading, the TPS output voltage would be way off. So i rotated the sensor back to it's original position, where it had the right output voltage reading and test rode the bike for the first time after all this and it ran a little better. it feels like the TPS is still off and it could run a little better. I.E. when i hold the throttle in the same position for a few seconds, it doesnt really start to "sputter" and feel like it wants more throttle all the time like my 07 does.

I havent yet ridden the bike with the tPS unplugged for comparison, but im sure it wouldnt run quite as good.

Did i do anything wrong? Do you think my TPS is okay and do these "extra" readings even matter? What should i do next?

[yamirider5588]

I thought you were chasing a jetting problem ... How did you narrow it down to the TPS sensor ?

[rhinoracin]

The TPS is not the only problem. it is a separate problem on my bike. 2 things happened to the TPS that threw it off. First, the previous owner of my bike removed the throttle stop instead of just cutting it down or getting the YZ part, unless it fell out. I somehow never noticed it missing for a few months. i found out not having a throttle stop can throw the TPS off or damage it. Then, during those few months where i didnt know much about the bike, i loosened the bolt that holds the sensor on the carb and rotated the sensor. i dont know why i did it, i just didnt really know what it was. After i knew i should check the TPS, i did and one of the readings was off and i could not fix it. I found out i should replace the TPS, so i did. Now im having the same problem with the new one. by the way, the part of the TPS i replaced is just the sensor part that attaches to the carburetor - the coil, wire, and coupler (all one part).

[yamirider5588]

So i rotated the sensor back to it's original position, where it had the right output voltage reading

So , this tells me you should move on to fine tuning the jetting . This too , is trial and error . Move the needle clip then test . Find the range that works best . There's not a direct answer I can give you . There's no substitute for good ole' wrench turning . You'll just want to change one setting at a time .

This is from http://www.thumperfaq.com/jetting.htm

Preparing for the Jetting Experience

Carburetor troubleshooting is simple once the basic principles are known. The first step is to find where the engine is running poorly. Remember the throttle position, not the RPMs, determine which circuit is controlling the mixture. Ideally, you would select the main jet first, then the needle and clip position, and then the pilot circuit. If the engine is having troubles at low rpm (idle to 1/4 throttle), the pilot system or slide valve is the likely problem. If the engine has problems between 1/4 and 3/4 throttle, the jet needle and needle jet (most likely the jet needle) is likely the problem. If the engine is running poorly at 3/4 to full throttle, MJ is the likely problem. While jetting the carburetor, place a piece of tape on the throttle housing. Place another piece of tape on the throttle grip and draw a line (while the throttle is at idle) straight across from one piece of tape to the other. When these two lines are lined up, the engine will be idling. Now open the throttle to full throttle and draw another line directly across from it on the throttle housing. At this point, there should be two lines on the throttle housing, and one on the throttle grip. Now find the half-way point between both of the lines on the throttle housing. Make a mark and this will show when the throttle is at half throttle. Divide the spaces up even again until idle, 1/4, 1/2, 3/4, and full throttle positions are known. These lines will be used to quickly find the exact throttle opening while jetting. Clean the air filter and warm the bike up.

On any circuit, if it is too lean it will pop and snap. If on the stand for the pilot or needle circuits, you can hear these best with the seat off listening through the air box. These are most often heard on deceleration but are sometimes masked by a WRF air cut valve. The air cut valve should be bypassed for proper jetting of the pilot circuit on the WRF. If you hear popping, too lean. A bog can be rich or lean but if it is not accompanied by popping, it is probably too rich.

[rhinoracin]

When i said the throttle position sensor had the right output voltage, that means only the output voltage was in specification. There was still one reading that wasnt right. I may be going too far here with the TPS, but i just want to have everything on my bike working the way it should. I know how a bike runs with the TPS plugged in and working compared to unplugged or not working, and i like it better with the TPS working properly.

Ive done a lot of jetting changes and tests on my bike, and i dont mind doing that because i know what needs to be done and most jetting problems i have come across i have been able to fix. It's just problems i cant fix right away and dont know the answer to, like my TPS, that i dont like and get in a hurry to fix.

If anyone wants to know what electrical meter im using, it's a small Cen Tech digital pocket tester that looks at least 5 years old. im not sure if it's even giving me the right readings, but i'll probably find out today becuase im going to use one they have at my store.

[yamirider5588]

Did it run the same with the TPS unplugged ?

[rhinoracin]

Before today, if i unplugged the TPS, it was hard to notice any difference. I think there was just more of a hanging idle when i revved the bike with the tps unplugged.

Today i went to my dad's dealership and got some help. I had 2 mechanics who have had experience with this help me out. First i found out there is nothing wrong with my electric meter. That was not the problem. We used my meter and a better one they had in the shop, and both gave the same readings for everything.

After wasting a couple hours playing with and testing different settings on the TPS, i could not get all the readings in the specified range at the same time. we tried everything we could. we pulled the sensor off the carburetor several times and stuck a flat blade screw driver in the "key hole" in the coil and twisted it around to change the way the throttle twists it (hard to explain). This made a difference, but there was only one other setting we could get it to. The first setting would be with just the full throttle coil reading not far off. That is what i had before today. Then twist the coil key hole clockwise until it has spring resistance again, and with that the closed throttle coil reading was off and the TPS output voltage was way off, but now the full throttle coil reading was correct. With both setting, if i rotated the sensor on the carb, the readings would still be off.

After testing the bike with the setting in which the TPS would read correctly in the full throttle range, the bike felt a little better to me. So i just left it at that. The bike runs fine either way and doesnt do anything weird, which is what the mechanics at the store said the bike does if the TPS is way out of range.

The mechanics who helped me didnt know what the problem was and they just said they've seen alot of problems with throttle position sensors, and the readings are not always going to be in the manuals specified range, and that's okay. They said the manual could be wrong about the specified readings. Does any of this sound right? I still need to see how the bike runs with the TPS unplugged, but im sure i will want to plug it back in. There's nothing wrong with any part of the throttle assembly in the carburetor..ive pulled it apart a few times and checked. Im not sure what to do now or if it's even a real problem. I might give Yamaha a call and see what they recommend i do.

Am i missing anything? what should be the next thing i check or do that could maybe fix the throttle position sensor?

[William1]

Does your bike still have the stock throttle stop (not one from a YZ)? If it does, you cannot open the throttle to full, it will only go to 3/4. Set the TPS to be correct at idle.

[rhinoracin]

No i dont have the stock throttle stop. right now the tps is set high at idle. the manual says it should be 0-3 (ohms?), but it reads around 3.9.

this is the only way i can get the full throttle reading within 4-6 ohms, which is what the manual recommends.

Since i have the choice of running the TPS with 1 or 2 different readings always off, what do you think should be the readings that are the most important to have set?

[Wayward Son]

set it so it reads right at WOT.

[rhinoracin]

Thanks Eddie...any other tips? I tested both my bikes with the TPS unplugged and the only differences was a bad hanging idle on my 07 and a little less WOT power on my 04 (the bike im having trouble with)

[rhinoracin]

does anyone else not notice that big of a difference when they unplug their TPS?

[Wayward Son]

no,ive never noticed anything effect on idle.

[rhinoracin]

Some mechanics i know said they often find throttle position sensors putting out wrong readings and they cant fix it. They said it's best to just get it working as good as you can, even if it's not perfect. Are they correct on this? ..i just want to hear more opinions on what i should do

[Wayward Son]

the main thing is to make sure its correct at WOT.