YZ250 Throttle Position Sensor (TPS)

LiftdT4R · Jun 13, 2009

I was looking through my Factory Service Manual and I noticied a section about the Throttle Position Sensor System. I have been having issues with the bike idling, even after rejetting the carbs. I was wondering if anyone knew what the TPS is, and what it does, it doesnt realy give a good explanation in the manual. I'm assuming it controls the powervalve? Maybe?

RM85rider123 · Jun 13, 2009

It ensures precise fuel/air mixing and extra-crisp throttle response throughout the powerband. I don't think it involves the powervalve. I guess this could be making a problem with your idle, but it is most likely something else.

LiftdT4R · Jun 13, 2009

RM85rider123 said:
It ensures precise fuel/air mixing and extra-crisp throttle response throughout the powerband. I don't think it involves the powervalve. I guess this could be making a problem with your idle, but it is most likely something else.

Ohh ok, I'm guessing this is done via the power jet in the carb?

RM85rider123 · Jun 14, 2009

LiftdT4R said:
Ohh ok, I'm guessing this is done via the power jet in the carb?

no, it is an actual sensor that does the work. Now you said you jetted the carb earlier, did you change the pilot jet?

LiftdT4R · Jun 14, 2009

RM85rider123 said:
no, it is an actual sensor that does the work. Now you said you jetted the carb earlier, did you change the pilot jet?

I did, I'm pretty familar with the carb, and most of the bike. Ive had a couple of Banshees over the years that Ive done all of my own maintenance on. I got the bike to idle decent, but I'm just wondering how or what the TPS does. Does it lean out or richen the micture? If so, how, via the power jet? I'm just not understanding the function it performs on the bike.

adam728 · Jun 15, 2009

The TPS works with the ignition to control the powerjet via the solenoid on the carb. The powerjet richens the mixture from half to full throttle, and below 8500 rpm.

Although I haven't read it anywhere, I would have to imagine that the TPS also has an effect on the ignition timing curve for acceleration and decceleration.

spark250 · Jun 16, 2009

If you think the TPS is at all out of whack follow the procedure in the service manual.

Each bike is set differently from the factory and sometimes they need adjustment.

From what I have seen the biggest sign of the TPS being misadjusted is a "hanging idle". Meaning if you rev the bike in neutral with no load it hangs kinda reving high and then maybe comes back down.

I can't remember the exact procedure but you slightly move the TPS on the carb to adjust it.

LiftdT4R · Jun 16, 2009

Thanks for the replies, good to know. Ive always had older bikes and Blasters and Banshees so Ive never seen anything like this.

Matt90GT · Jun 16, 2009

TPS = Throttle Position Sensor

If you think you are having issues with the TPS, simply unplug it and run the bike. With it unplugged, the CDI will revert to a 2d ignition mapping. Meaning you will not get all the benefits of the timing advance. Wen it is plugged in, the CDI will run a 3d mapping mode.

YZ250 Throttle Position Sensor (TPS)

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