I checked all 94 posts regarding TPS, some good info but I could not find what I am looking for:

What is the function of TPS?

Does it need adjustment – how do you diagnose the symptoms for a need to adjust TPS?

The book has good instructions on checking and adjusting TPS – any additional info is welcomed.

I have a 99 WR, is there a need (or possible) to adjust the accelerator pump? How?



The TPS is a throttle-positioning sensor.

In nearly all cases, these are used as a means for an ignition control module (usually containing some form of computational logic) to determine the positioning of a carb slide or valve body opening in respect to and from off-idle, idle and full throttle.

In this bike, the information is sent to the CDI to adjust the timing of the spark. Throttle positioning, of course, is a better predictor of what the needs of a rider are, to that of engine RPM.

In many cases, most logic units contain what is called a two or three dimension "map", which is essentially a controlling plot of engine dynamics to that of rider and engine input.

On these bikes, the only considerations to the map are RPM and TPS. More sophisticated maps would include engine temp and exhaust gas analysis as well.

The law of the manual says never move the TPS out of spec. This is because it’s nearly impossible to improve on the needs and purpose of this, as one would do with say jetting.

On this bike, I have never experimented with different TPS positions. On more sophisticated machines, I usually moved the TPS to shift the positioning of the controlling unit map to provide a quick means to better performance, (usually in cases where the map is designed for street or EPA considerations). Of course, one should just modify the map, but in some cases you don’t have access to it, or not enough access for fine-tuning.

I would say it’s okay to experiment, but under the rule that nearly any adjustment will have a corresponding sacrifice.

As for the accel pump, there’s been plenty of talk about modifying this. For this, it’s a matter of when and how much. I run a .8 sec spray that begins at ¼ throttle. However, it’s all in a matter of what your needs are to your style of riding and bike setup. See the threads on BK mod for more details.



Thank you for the explanation. I just checked the resistance and it is 6.04 ohms which is within spec. So I left it alone. I checked the accelerator pump assembly and diaphragm and to my astonishment it was packed with junk. I cleaned it and clean the carb also. My bike was running kind of ratty (rich - the plug was covered with sooth). I am hoping that by cleaning the carb the problem is alleviated.


By the way, you may have seen some earlier posts about how carb cleaner reacts with the rubber used in the acceleration pump diaphragm.

It causes it to swell, and the unit won't function when you put it back together.

Letting it air out for a day seems to remedy this, or just don't let the carb cleaner make contact with the rubber.


[ November 19, 2001: Message edited by: DaveJ ]


I used allot of carb cleaner. I used compressed air to dry it out and then assembled the parts. So it will fail soon?


I've had other carb parts swell after being soaked with carb cleaner (haven't taken my 426 carb apart yet) and in my past experiences soaking them in gas seemed to help them get back to original size. Now knowing better I try to avoid getting cleaner on the parts completely, but if it went back together and it's in contact with gas them maybe it will be OK.

The carb clean gets into the rubber and causes it to swell. You can dry it all you want, but it does no good. Must be some sort of reaction.

I usually just let it sit overnight and it comes back to normal. Not sure if that would still work if in the bike.

Perhaps Sirthump's idea would be the ticket.

If you want a quick fix to getting the diaphram back into normal shape after using carb cleaner, just wash it with warm water and dishwashing liquid. It becomes soft and pliable again in a few minutes and regains its normal shape.

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