TPS compensation for worn throttle shafts

[Doansci]

This might help someone.  (and apologies if it has already been noted) 

I had carefully set the TPS by the book and the bike (2002 LeMans) suffered from surging when hot and abrupt on/off throttle transition and slight pinking at full throttle.  The surging and throttle transition made the bike frustrating to ride.  I retested the TPS it was still 160mV with throttle plate closed = not significantly different than where I'd set it last year.

I then noticed that when the throttle was pulled open that the first motion was to take up throttle shaft wear.  (to check for wear, grab the throttle shaft nut under the throttle body and move it side to side.  The right side has more play that the left, perhaps because of the return spring.  There are rubber seals on the shafts but may be unable to compensate for the wear or have failed after 23 years.)

In one of the TPS discussions KiwiRoy suggested that because the voltage increase with rotation is not linear that the goal of setting the TPS was not so much to achieve precisely 150mV (or 157mV), but to make sure the setting was on the tail of voltage increase.  I pictured the voltage increase as a curve similar to exponential growth with 150mV somewhere close to the baseline suggesting that at 150mV the computer can sense the TPS but is not yet altering fuel settings.  After setting the TPS the manual states that throttle plate angle should be set to 3-3.5 degrees.  I wondered how to do this because I don't have Guzzidiag computer setup, but another post (I forget who posted) stated that throttle plate angle at idle corresponded to 470-480mV.  Another post stated that instructions for installing a new mixture map that the idle throttle stop should be set at exactly 475mV.  My idle stop was at 311mV so I decided to experiment with changing it.

I set the TPS to show about 470mV just as the throttle starts to lift off the idle stop.  As the throttle linkage is pulled the first movement takes up play in the worn throttle shaft and the mV increases. All the play is taken up and the throttle starts to open at about 470mV but my TPS reads about 420mV when the spring holds the throttle against the idle stop. (differing amounts of wear should result in different idle stop mV)  With the throttle plate fully closed (as in setting by the book) the TPS shows about 220mV.  I then balanced throttle bodies side to side.  

The result is dramatic!  There is no hint of surging even at low rpm and low speed and the harsh on/off throttle transition is mostly gone.  There is no pinking.  It has really improved the bike.  

Yes, I know there someone has posted a tutorial for replacing throttle shaft bushings.  I have even bought new bushings and seals and will get to it eventually, but I am very happy with the way the bike runs now.  

    

[Lucky Phil]

7 hours ago, Doansci said:

This might help someone.  (and apologies if it has already been noted) 

I had carefully set the TPS by the book and the bike (2002 LeMans) suffered from surging when hot and abrupt on/off throttle transition and slight pinking at full throttle.  The surging and throttle transition made the bike frustrating to ride.  I retested the TPS it was still 160mV with throttle plate closed = not significantly different than where I'd set it last year.

I then noticed that when the throttle was pulled open that the first motion was to take up throttle shaft wear.  (to check for wear, grab the throttle shaft nut under the throttle body and move it side to side.  The right side has more play that the left, perhaps because of the return spring.  There are rubber seals on the shafts but may be unable to compensate for the wear or have failed after 23 years.)

In one of the TPS discussions KiwiRoy suggested that because the voltage increase with rotation is not linear that the goal of setting the TPS was not so much to achieve precisely 150mV (or 157mV), but to make sure the setting was on the tail of voltage increase.  I pictured the voltage increase as a curve similar to exponential growth with 150mV somewhere close to the baseline suggesting that at 150mV the computer can sense the TPS but is not yet altering fuel settings.  After setting the TPS the manual states that throttle plate angle should be set to 3-3.5 degrees.  I wondered how to do this because I don't have Guzzidiag computer setup, but another post (I forget who posted) stated that throttle plate angle at idle corresponded to 470-480mV.  Another post stated that instructions for installing a new mixture map that the idle throttle stop should be set at exactly 475mV.  My idle stop was at 311mV so I decided to experiment with changing it.

I set the TPS to show about 470mV just as the throttle starts to lift off the idle stop.  As the throttle linkage is pulled the first movement takes up play in the worn throttle shaft and the mV increases. All the play is taken up and the throttle starts to open at about 470mV but my TPS reads about 420mV when the spring holds the throttle against the idle stop. (differing amounts of wear should result in different idle stop mV)  With the throttle plate fully closed (as in setting by the book) the TPS shows about 220mV.  I then balanced throttle bodies side to side.  

The result is dramatic!  There is no hint of surging even at low rpm and low speed and the harsh on/off throttle transition is mostly gone.  There is no pinking.  It has really improved the bike.  

Yes, I know there someone has posted a tutorial for replacing throttle shaft bushings.  I have even bought new bushings and seals and will get to it eventually, but I am very happy with the way the bike runs now.  

    

The TPS voltage change is not an exponential curve but a straight line. Depending on the model of TPS it is either a dead straight line from zero degrees to 87 or a straight line until a break point at 30 deg then another straight line from there. So either the linier or non linier version.  

Just change the throttle bushes and seals. Delaying replacing the coated bushes will just end up wearing the throttle shafts and then the TB's are scrap unless you have the kind of access to machinery I have. Use the Viton seals now available via CA cycleworks as they will be better than the yamaha seals I'm sure.

Phil

Edited July 8 by Lucky Phil

[docc]

It is interesting to note that the later "CARC" set-up indexes the TPS with the throttle bodies seated on the factory pre-set idle stop (The Sacred Screw) in "similar fashion" to @Doansci's approach.

Using the V11 "completely closed" index is curious since, once the linkage is hooked up and the idle set, the ECU never sees any values below the idle setting. It is simply the established method to index the map to the physical throttle opening through the rest of the range to WOT. Can the same indexing be achieved using the throttle angle at idle and the TPS at "some" mV? Sure, but it is going to be hit or miss.

Seems @Doansci got a hit!

(YMMV)

P.S. - I am due a fresh Decent Tune-up and will pay attention to where my throttle degrees opening and mV end up at idle . . .

[gstallons]

2 hours ago, Lucky Phil said:

The TPS voltage change is not an exponential curve but a straight line. Depending on the model of TPS it is either a dead straight line from zero degrees to 87 or a straight line until a break point at 30 deg then another straight line from there. So either the linier or non linier version.  

Just change the throttle bushes and seals. Delaying replacing the coated bushes will just end up wearing the throttle shafts and then the TB's are scrap unless you have the kind of access to machinery I have. Use the Viton seals now available via CA cycleworks as they will be better than the yamaha seals I'm sure.

Phil

Where do you source these parts ?

[docc]

28 minutes ago, gstallons said:

Where do you source these parts ?

 

[docc]

On 7/8/2025 at 11:14 AM, Doansci said:

  After setting the TPS the manual states that throttle plate angle should be set to 3-3.5 degrees.  I wondered how to do this because I don't have Guzzidiag computer setup, but another post (I forget who posted) stated that throttle plate angle at idle corresponded to 470-480mV. 

    

Taking a closer look at the Workshop Manual, the degrees opening of the throttle plate at idle is 3,6º +/- 0,5º (3.1º - 4.1º).  The corresponding mV I have written in the margin for this range is 5.10 - 5.38 mV. Pretty sure I got this from Ed Milch very early on.

The Workshop Manual states this setting should yield an idle of 1050 +/-50 rpm and that, if it doesn't, to set the TPS to 150mV +/- 15.

First of all, that is a ridiculously wide range for the TPS baseline (135 - 165 mV). I ran mySport at the top end of that range back in the early days and it does not run well (thinking, at the time, "I'll just add more fuel by turning up the TPS.")

Certainly, the best results indexing the mechanical throttle position to the mapping is to baseline as close to 157mV as possible and balance the throttle bodies at "some" rpm.  Accounting for my worn throttle shafts (and bores and plates), I used this (rather intimate) method to hold the throttle plate closed after pressing the bottom of shaft toward the other throttle body, along the axis of the throttle connection rod. Out for a shakedown ride after the throttle body balancing, she seems quite happy with the outcome . . .   

Idle preference is another matter. Once all tuning parameters are addressed (including setting the CO Fuel Trim, which cannot be overlooked), put your idle wherever you and your V11 are happiest. In these high ambient temperatures (90-95ºF/ 32-35ºC), and owing to my well worn flywheel teeth and gearbox input hub teeth, I prefer my idle toward the 1500 rpm mark; much less rattle at idle, more stable if stuck in traffic, and more oil for cooling, methinks.

[Just a quick reminder that the factory tachometers, especially the early white-face Vague-liar are known to read up to 300-500 rpm high. In the event the tach is used to set the idle at 1000 rpm (1050 minus 50), the poor thing is trying to stay alive idling at 500-700 rpm. ]

 

[Kevin_T]

I went and rebuilt my throttle bodies they were leaking gas pretty good. Phil mentioned when he rebuilt his one of them was missing the rubber seal altogether. So, I thought I would dig into mine. The leak was just the injector needing some cleaning, but I was in there already, so I replaced the bushings. When ordering the bushings its clear they're made to run at some low rpm they have a running class fit. Don't think that they're going very tight at all. I guess it helps with the throttle return having the throttle impeded might for no more posts.

[audiomick]

On 7/13/2025 at 1:45 AM, docc said:

factory tachometers, especially the early white-face Vague-liar are known to read up to 300-500 rpm high. In the event the tach is used to set the idle at 1000 rpm (1050 minus 50), the poor thing is trying to stay alive idling at 500-700 rpm.  

 

Which is all the more reason to use Guzzidiag to set the idle speed. 

[docc]

5 hours ago, audiomick said:

Which is all the more reason to use Guzzidiag to set the idle speed. 

Agreed. In this way, you can see what rpm the ECU (map) is seeing, and know what your specific correction value is to what the tachometer displays.

The accuracy of my Speedhut conversions has spoiled me, though . . .