blue wire and bk and tps mod on yz450f

12 replies to this topic
  • falshh

Posted April 18, 2004 - 09:18 AM


Ok I have a stock 04 yz450f It really has plenty of power but I guess free horsepower wont hurt.I just wonder by disconnecting blue wire and the tps sensor why did Yamaha put it there in the first place.I think people have said the blue wire reduces peak rpms at nuetral, is this just from guys overrevving it?The tps Ive heard guys say because that is what the carb came with it so yamaha just hooked it up, this sounds weird to me there must be a better reason for having it.Well any input will help guys.
OH yea what is the bk mod , is it for bog on the bike and a carb mod and is it needed on the 450, Ive never felt a bog?

  • aford541

Posted April 18, 2004 - 12:32 PM


Regarding the TPS I think the reason for it is in Europe the FIM limits the octane to 89 The TPS must reduce the amount of initial advance allowing the owner to run whatever fuel is available. I did the bk mod on a 03 YZF and there really was no difference, the bk mod reduces the time the accelerator pump sprays.
I don't think there is any performance advantage gained by disconnecting the blue wire so mine is still hooked up.

My bike has a power now and the TPS sensor UN plugged and it hauls.

  • chrome-crf

Posted April 18, 2004 - 12:54 PM


So does this mean that if you disconnect the TPS sensor it will help out a little :). What about the neutral switch? What the hell does that thing do. The information in the manual isn't too helpful.

  • Satch0922

Posted April 18, 2004 - 02:01 PM


the TPS disconnected gives a smoother (no dip) powerband and about 2hp on a 450F. I have it disconnected on my 426 and it felt like the bike pulled harder in the low to midrange of the powerband. No data to back this up though.

The neutral switch changes the rev limiter so that the bike can't be over reved while it's in neutral (on the stand). This does not by pass the rev limiter all together. Also on older bikes (400/426) it was thought to give a weaker spark when the bike was in neutral. Alot of people disconnected it to aid in the starting of the beasts (disconnected the ignition "thought" the bike was in gear and gave full spark). Not sure if this theory has ever been proven but alot of us disconnected the neutral switch and the bike "appeared" to start better. :)

Both of these mods are free and easy to try. Disconnect them if you wanna check it out and if you don't like them then you can easily hook them back up.

  • RatRacer

Posted April 18, 2004 - 05:47 PM


I have a WR450F with the YZ cam & tried disconnecting the TPS today; I found the throttle to be much more linear & when decelerating it wasn't backfiring as much.
Power increase? Maybe but regardless it's an improvement so I'm leaving it disconnected.
2 Thumbs Up :) :D

  • the go-devil

Posted April 18, 2004 - 11:01 PM


I unplugged the TPS on my YZ cammed WR450 too. After getting some riding time on it on sloppy ass mud and nasty trails, I'm going to leave it unplugged. It has a much smoother transition from the low end to mid range. No more "hit", except everything above idle :). I can't even imagine how th YZ's are without the heavy rotor.

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  • Anssi

Posted April 19, 2004 - 08:36 AM


in Europe they run 87 octane fuel

Yeah, sure, IN ALBANIA.

  • revolucien

Posted April 19, 2004 - 10:10 AM


for the neutral sense switch, the bike is set to have a lower voltage to the spark plug when the bike is in neutral, doing this FREE mod is supposed to bump up the voltage while in neutral. this is not only supposed to help starting but, also increase performance check this link for more info.. http://www.thumperfa...m/blue_wire.htm i haven't done it yet but, will be doing it this week.

  • fatmancantfly

Posted April 19, 2004 - 01:09 PM


The sky blue wire has a single pin connector at the front of your frame just under the tank. Follow the wire from the switch (just under your shifter) up the front of the bike.
The BK mod does help your bike accelerate quicker. All bikes differ a little on fuel spray duration. Mine was 2 full seconds. That's way too much. When your on and off the throttle a lot, your putting way more fuel into it than it needs. The BK mod limits the fuel spray (after you adjust it) to where the motor is only getting what it needs to help acceleration. This also saves fuel (very helpful with a 1.8 gallon tank). Look at the picture on "thumperfaq" for an example. I epoxied a stopper inside the carb cover and then filed it down to where it would only allow the cam to move a little giving me a 1/2 second of fuel spray.
P.S. I hope you stopped flogging the throttle on the stand. :)

  • falshh

Posted April 19, 2004 - 02:37 PM


yea thanks for the input on the flogging the throttle on the stand that really made sense of the rich mixure signs I was getting , I took it riding this weekend and got to open it up in all gears and with a new plug it was running great.

  • 2004yz450f

Posted April 18, 2009 - 07:55 PM


Can I remove the tps sensor and still run 89 octane fuel. Will this mod help or make my horsepower worse on my 2004 yz 450? Also, what would be the best mod to this bike to improve power and economy.

  • grayracer513

Posted April 20, 2009 - 08:55 AM


Much of the info contained in this 5 year old thread is conjecture and/or inaccurate.

The function of the TPS is to provide throttle load information to the CDI so that the timing can be advanced during part throttle operation for increased engine efficiency and overall crispness at cruising speeds and other less than full throttle situations, disconnecting it will not improve, or even really change, full throttle operation at all unless there is a fault in the TPS or the way it's adjusted. It also has nothing at all to do with compensating for lwoer grade fuels or anything of that nature. The bike will run better with it.

Likewise, the "blue wire mod", which disconnects the lead running to the neutral switch, has no effect on engine performance in the least. The blue wire alerts the CDI that the bike is in neutral when it is grounded by the switch. The CDI responds by retarding the timing slightly so the bike will start more easily, and by lowering the rev limit to 7000. Since the wire essentially IS disconnected any time the bike is in any gear, the mod has zero effect on performance. It may, however, make your 450 harder to start, and it may cause it to kick back so hard you'll think you were shot in the bottom of your foot.

The best mod for performance and and economy is to have the engine jetted correctly through the entire throttle range, and to be certain the CDI and TPS are performing as they should be.

  • jjj109

Posted April 20, 2009 - 09:26 AM


Grayracer is completely right. I spoke with my cousin , he is the top tech at his dealership where he works. He told me by disconnecting the tps will make the bike only use part of the ignition mapping and have no performance gain what so ever. The cdi needs the tps to feed it info to give the motor the correct ignition timing to perform at its peak. Disconnecting it will just limit the bike potential :p

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