TPS experiment results

5 replies to this topic
  • Shawn_Mc

Posted July 27, 2002 - 05:58 AM


If you read my other post, you are up to speed if not, Ill recap.
I played with the rotational setting of the TPS on the carb. I found that if you rotated it back and fourth with the engine running, it effected timing at idle. My conclusion is this, if you have access to good (race) gas, you want to play with this setting.
I found that if I rotated the TPS counter clockwise about 2-3 minutes on the face of a clock, the idle rose significantly. This is the location that I left it at. Highest idle speed.
After resetting the TPS I needed to readjust the idle back down a tad. I also decided to play with the mixture screw. I found that if I leaned the mix, it idled smoother, and revved cleaner. So I did that too.
Result: Bike pulls cleanly off the bottom with solid predictability, was easier to start, and was crisper through out the entire range. I also found that a little popping on decel would go away when the bike was fully up to temp. This wouldnt be the case prior to the TPS adjustment and the same mixture setting on the pilot. I believe the reason for the popping is an artificially high idle, caused by insufficient advance timing at idle, disallow the lower throttle setting at idle. With the ignition timing just slight advanced, you can reduce the throttle opening for the same idle speed, and thusly reduce the fuel, because the throttle setting is lower allowing less air, and actualy a higher vaccum pulling as much or more fuel at the same RPM, becaue of the lower throttle setting.
If you want to try this mod, go for it, its easy, and you can always put it right back, if your TPS is marked properly.

I dont know if you could do this with pump gas. I run 100 octane unleaded. IF your running pump gas, doing this mod may produce detonation, but I have the feeling that it might not be all that harsh, and it may be no big deal. But use a careful ear anyway. If you have access to race gas and run it, do this mod, your bike will be quite a bit smoother.
Final settings were as follows:
Pilot 45, 3/4 turn on the screw
Needle: stock 2000, #3 postion
Main: 168
200 feet above sealevel (Saddleback)
85 degress 74% humidity.
Im stoked, and Im leavin it! :)

  • John_Lorenz

Posted July 27, 2002 - 06:06 AM


SO would you perfer this mod over the Powernow Add-on
Ha just kidding

I may just do it today, I am runing 76 100 also, I will be riding on Tuesday though.

Thanks for the info...Good work

  • Chris_from_Oz

Posted July 27, 2002 - 06:55 AM


Hi Shawn, I have tampered with the TPS on my Hornet, and had similar results to you, my bike ran best using half premium unleaded, and half BP100 (local av-gas). I'll be honest and admit I never even thought of doing it on my 426, but now that you've posted your findings, I will, thanks.

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  • Boit

Posted July 28, 2002 - 01:48 AM


Great info Shawn. Since I also have a '00 and use MR2 fuel, I'm itching to experiment with the TPS setting. I'll make sure to make an index mark before moving the TPS.

  • DaveJ

Posted July 28, 2002 - 09:28 PM


Yes, ditto. Great work.

It's good to get stuff like this posted for future readers to search on.


  • Shawn_Mc

Posted July 29, 2002 - 07:18 AM


My first test was at saddleback, a fairly tight course that doesnt really let ya ring it out too much. I went to Elsinore on Sunday the 28th. Its has some places where you can really let it run. I found that the thing pulls really really hard from the mid on up. Which puzzles me, I didnt think that the TPS adjustment would effect that, but it could be the idle screw being leaner leaning the mix just a bit, and letting the thing pull like a truck.
Guys with the Thunder Alley pipe: Dont make the mistake of jetting it too fat. It gets lazy on top. Ive got mine where the pipe is just the slightest gray at the end cap, and it runs really hard. Im very happy. Best 20 bucks Ive spent, and that was on the tool.

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