Switch for TPS

92 replies to this topic
  • bg10459

Posted July 19, 2009 - 09:05 AM


Let's say the stutter occurs mostly at 1/2 throttle. You make a device (easy enough to do) to 'shift' the TPS signal 25%. If in fact the issue was merely the TPS signal, the stutter would be moved to 3/4 throttle.

I'm not certain it would just move because

...the way the CDI works is it expects values (RPM TPS = X) to always be in a certain range.

You're only changing one variable (the TPS signal) which would create an entirely different set of X's. I'm also only suggesting maybe a 1% shift. This might keep the X result on the map to prevent the fail safe mode, but also prevent the X result from falling between two points on the map, which is what I think most people are attributing the studder to.

Bottom line is, when everything seems to be working properly, on a bike with the Grey wire disconnected, there is a range of throttle positions and RPMs that have the stutter. To not have the stutter, (at least so far in the testing) it appears you must change a variable.

I'm not sure I follow you here. Are you saying I must have changed a variable, or I just haven't found the studder yet?

This is so much more interesting than a "which oil" tread. :worthy:

  • William1

Posted July 19, 2009 - 09:48 AM


It is kind of hard to explain in a thread but.... For the CDI to provide the ideal spark advance, it takes the TPS signal and rpm. These are combined in an algorithm that spits out a value use to figure the amount of advance. If the value is out of a predefined range, the CDI ignores the calculated value and use a flat single default value for the advance. There are times when the default value is perfect, there are times when it just kills the power. If the TPS is providing a different signal than it should, more often, the CDI will fall into the default value.

Most of the examples I gave are broad stroke concepts. I'd need to write a 'white paper' to accurately define all the functionality and logic.

Not all riders complain of the stutter. I cannot explain why this is. I can guess however. But guessing could be extremely incorrect.

  • Thumper_Bloke

Posted July 19, 2009 - 08:44 PM


But guessing could be extremely incorrect.


  • William1

Posted July 20, 2009 - 03:29 AM



And the purpose of this is? Is it really useful?

If you have a valid comment, make it. If not, then what is the point?

  • Thumper_Bloke

Posted July 20, 2009 - 01:53 PM


I just don't like the idea of disconnecting or fooling the TPS signal. It will land you on a map that is not ideal almost all of the time. I'm just sayin.

  • William1

Posted July 20, 2009 - 02:22 PM


Ah, I understand. And I agree. But the purpose of this thread and mod is to make a bad situation bearable. Just enough to go between trail heads, not for on road. Many DS riders like me, do less than 5% (I probably only do 1%) on road miles. For the amount of time we are on the road, the expense of a aftermarket CDI is not justified. The performance loss we will experience fooling with the TPS will be insignificant compared to the reduction in annoyance. We will hit the road, get to cruising speed, flip a switch, get to the next trail, hit the switch to re-enable the TPS and go on our way. Cost will be a pair of connectors, a switch and some wire, maybe a few resistors. As I said earlier, if I were a SM rider or someone who spent a fair amount of time on the road, the CDI change makes more sense.

If you had a one mile driveway, which makes more sens to buy to get the mail, a golf cart or a Ferrari? Sure the Ferrari is more fun but the golf cart makes more sense.

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  • Chas_M

Posted July 20, 2009 - 04:10 PM


Based on the results I got and expect to get from my (guinea pigs:moon: ) generous testers, this is what I think we will want to do:
No need for the resistors and all the wires, double pole triple throw switch.
A single pole, single throw switch on the yellow wire. Still considering options to make this setup 'factory', but it will be very simple and all the parts should cost under $50.00 at most and a cheapo solution could be about $10.00

Just to reiterate, referring back to my original post on 02/21/09 where I had installed a single pole on/off switch on the TPS yel wire on both of my KTM's and noted little if any seat of the pants differences, although with the switch off, the engine response may be slightly less abrupt.

I might also note that I get absolutely zero 'stuttering' with either of my bikes, with or without the TPS under any condition.

I'll add one question here. With the TPS unplugged or with the the yel wire 'switched off', why wouldn't the CDI interpret this as a no-load condition and add full TPS advance to the default advance curve?

  • William1

Posted July 20, 2009 - 05:00 PM


Never heard of a YZ or Honda stuttering either, just the WR's, a Yamaha glitch I guess.

The CDI expects values to be within a certain range. With my resistor setup, it sees a TPS signal as 3/4 throttle (good or bad, testing will decide). At a point prior to and after this value, combined with RPM, the algorithm will be out of range and default to a set value. Same as what would occur if the TPS were disconnected or the Yellow wire unplugged (though I am assuming this last part as I have not test it with just the yellow undone). Finally, with the TPS showing a full closed throttle, a signal voltage is sent to the CDI (+.62V, -4.6V), disconnected would be zero on both, very different.

It stinks so much of this is guess work. Unfortunately, not all CDI's use the same logic so rules vary somewhat. So a lot of guesses and (hopefully) intelligent assumptions are being made. But the bottom line is a cheap solution to a minor issues for dual sporters who rarely ride on pavement.

  • racinteach

Posted August 05, 2009 - 10:17 PM


I get from this as well, that cutting the grey wire may actually make the stuttering worse... I just sumoed my bike for weekend road rides..and yes the off idle input sucks, but I also notice the constant throttle on issues..unles wide open I notice it..

  • ASternad

Posted August 18, 2009 - 10:32 AM


Can a CDI from a YZ be used in a WR, would that even help?

  • William1

Posted August 18, 2009 - 10:58 AM


Can a CDI from a YZ be used in a WR, would that even help?

Sadly, no unless you make significant woring changes. The YZ CDI runs straight off the stator (AC), the WR runs off the battery (DC).

Testing has show the stutter is much worse with the Grey wire cut. The TPS switch seems to make a small improvement if the Grey wire is connected and a big improvement if the Grey wire is cut. Hard to say here but what I mean is, with the TPS disconnected, the stutter you would feel with the Grey wire cut is identical to the stutter you have when the Grey wire is connected and the TPS is disconnected.

Easy enough to test on your own. Ride with the Grey wire disconnected. Ride with it connected. Do both these tests again, but with the TPS disconnected.

  • thedktor

Posted March 02, 2010 - 11:21 PM


Any update on this? (haven't been on the forum a while)

I had mine jetted to fix the stutter: 170 main, needle, UDS #4, #48 pilot.

Stuttered a bit on last few rides (wet and cold) so dropped the needle a notch (#3) and fixed.

- Steve

  • grayracer513

Posted March 03, 2010 - 10:54 AM


Electrically, as long as the TPS signal voltage to the CDI is zero, there's no difference. I would put it on the input to the switch, myself, but as I say...


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