TPS Installation


9 replies to this topic
  • savagex

Posted January 17, 2013 - 12:31 AM

#1

Hi Guys,

I just put a new main jet in my 2009 YZ450, when I removed the carb I also took off the TPS (doh!).

I am about to put the carb back on and wanted to know some information on how to properly set the TPS. There is still a green factory pen mark on the carb and TPS, but it is a thick line and I am not sure if it will be accurate. I read the adjustment process in the manual on page 6-10, It seems very involved.

Could someone further explain this step:
7. Insert the thin electric conductors"2" (lead) into the throttle position sensor coupler "1", as shown, and connect the tester to them.

Has anyone documented this with images or made a video of TPS adjustments?

This youtube video shows a way to check the carb before you install it. Is this correct, if you do this do you also have to perform the adjustment on the bike?

What will the happen if the TPS is not set correctly? What should I look out for?

Thanks for any help.

Attached Thumbnails

  • -1.jpg


  • grayracer513

Posted January 17, 2013 - 08:14 AM

#2

The picture from the manual is a little misleading because it shows the connector as unplugged from the harness. For the test being described, the TPS must be plugged in and functional, with the voltmeter leads inserted as shown. This is called "back probing" the connector. What you are being asked to do is to run the engine with the meter connected and read the voltage at those two wires at an idle, with the desired voltage being between .58 and .78 VDC.

The reason for the test is that the CDI bases its mapping on the voltage it actually receives from the TPS, and that is dependent not only on the resistance of the potentiometer within the TPS, but also on the output from the stator. Since both of these can vary independently of the other, the only accurate way to set the TPS is while it's running.

If you've had the carb off your bike already, you will already realize that this is going to be a monumental pain in the ass to adjust because of the limited accessibility of the TPS with the carb in place. A really seriously devious way to do this is to run the engine off of a substitute carb while you hold the real one in your hand, TPS plugged into the harness, and adjust it.

The video is no help because it is measuring resistance, which only shows that the TPS itself is OK. It won't help in adjusting it. Rather than using the paint mark, or in addition to it, use the "witness mark" left in the plastic of the TPS flange by the retaining washer and screw. It will get you very close to where it originally was.

  • stevethe

Posted January 17, 2013 - 09:40 AM

#3

I thought you could adjust for the proper idle speed with the bike running. Then back probe and set the throttle position sensor with it off. That's the way I did it on my WR450 don't know if they are any different. Could be different since the WR has a battery ?

  • savagex

Posted January 17, 2013 - 10:12 AM

#4

Thanks grayracer.

If the TPS is not in the correct voltage range, how will the bike perform? What signs should should I look for?

When they say the leads "need to be inserted" does that mean they need to pierce the wires? I am a noob to electrical work.

  • grayracer513

Posted January 17, 2013 - 11:17 AM

#5

I thought you could adjust for the proper idle speed with the bike running. Then back probe and set the throttle position sensor with it off. That's the way I did it on my WR450 don't know if they are any different. Could be different since the WR has a battery ?


The battery provides operating voltage without the engine running. This doesn't happen with a YZ.

If the TPS is not in the correct voltage range, how will the bike perform? What signs should should I look for?

When they say the leads "need to be inserted" does that mean they need to pierce the wires? I am a noob to electrical work.


The TPS is used to advance the timing farther than normal during part throttle operation. How a simple misadjustment of the TPS affects the performance depends on how big the error is and in which direction. The bike could potentially ping at part throttle, or seem "soft" and unresponsive/ not "sharp". It may also stutter or misfire at a steady cruise. I should mention that usually a defective TPS will cause a lot more trouble than one not adjusted correctly will.

As you look at the back side of the connector where the wires enter it, you'll see a rubber seal between the wire insulation and the connector shell. Your VOM leads should be inserted between this seal and the wire so that the probes slide under the seal to contact the metal of the terminals in the connector. You may need to use something thinner than your VOM lead probes to accomplish this, but piercing the wires should not be necessary. You should avoid doing so if at all possible.

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  • CO_Rider

Posted January 18, 2013 - 05:44 PM

#6

I found it to be a real pain to try and get the leads in there and try to hold them in place like gray mentioned. Try some safety wire, a couple of smaller paper clips (regular ones not with the little wrapping) or something of the sort. If you have the clamp style leads then just clamp on. If not you could make a "loop" to hold the leads. This will save you the pain of wanting to light your bike on fire since you won't have to try and hold the leads in that tiny little clip while trying to adjust in the very very and I mean very limited space! LOL

  • savagex

Posted January 26, 2013 - 01:23 PM

#7

Thanks for all the tips, the bike seems to be running correctly. I put the TPS back in the same spot as the factory mark, need to get my multimeter out and check it just to be sure but it seems to run fine. I got rid of the annoying backfire on deceleration with a new jet.

There is one weird random issue I am having, I feel a slight electrical shock, once or twice per lap, on my front break lever. Any ideas what may cause this? I cleaned the spark plug rubber ignition coil. That and the TPS would have been the only thing I touched that were electrical. I changed gloves while I was riding to see if that was an issue but it didnt help.

  • grayracer513

Posted January 26, 2013 - 01:55 PM

#8

I feel a slight electrical shock, once or twice per lap, on my front break lever. Any ideas what may cause this?


Kill switch shorting to the handlebar would be a likely suspect. Probably through water or? under the switch rather than a direct, metal-to metal short. That happened to mine one day, but it quit doing it before I had a chance to figure it out.

  • moto116moto

Posted January 28, 2013 - 12:14 PM

#9

Gray, I need to adjust my TPS on my 08 yz450f due to the previous owner idiotically unplugging it from the carb while rejetting. You said the best way to do this is to use a substitute carb while holding/adjusting the real carb in my hand. For the record, i have a different carb i can use as a substitute. But is the reason I want to use a substitute carb because there's no room to adjust the tps while the carb is attached?

  • grayracer513

Posted January 28, 2013 - 12:33 PM

#10

Yes, it is. You first need to set the idle speed on the "real" carb, pull it off and install the "sub" carb, and run the engine while adjusting the TPS on the "real" carb (plugged in and all that). You can also loosen the TPS so that it can be moved, but will stay in place. The trouble is that unless you make a tool for it, you have to remove the carb to loosen the sensor, and then again to tighten it, same as if you use a sub carb.

But there is no need to adjust the TPS simply because it was disconnected electrically as long as it was not physically removed or repositioned. And disconnecting it electrically isn't altogether idiotic, either. Just depends on why and what he was trying to accomplish.





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