Hello forum, I'm new here, I would appreciate the help.

[facundo duarte]

Hello people, I am facundo, sorry for my English, I am using a translator. I recently purchased a 2000 DT125R with about 21,000 miles. After a carburetor cleaning, I moved the reed switch aside and removed the two pieces from the inside of the exhaust. The problem is the following: the bike reaches the power band but it is short, it does not exceed 9.5k, it seems like an electrical cut but I have doubts if it is rich. Before submitting to the forum, I read everything I could find about the problem on different forums and looked through it, but no luck. I already replaced the spark plug, cap and Ht, I also did the side stand thing, I already measured the fuel level in the carburetor and it was within range, the PV is working correctly and I checked it. The battery is new and its connections are good. Original carburetor with its jets corresponding to the model, main jet 240 and pilot 25. I need help, where I am from there is no information and almost none of these motorcycles, any suggestion would be appreciated, greetings.

[facundo duarte]

I add that it has 3rm-20 cdi, 3mb00 cylinder and 3nb cylinder head. chassis code de031 and under the seat it says 3rmj-030. I also want to thank everyone for all the information shared on the forum that I read previously and it helps new owners like me a lot.

[Calum]

Hi there bud,

Sounds like a reed switch issue to me, or powervalve.

I've never done it myself before, but my understanding there seems to be two different ways of doing the reed switch, so double check that the reed switch has been applied correctly.

The other thing that causes this exact problem is where by the Powervalve closes in the higher RPMs limiting power. This is really easy to test to eliminate rather than figuring out the reed switch problem.

Allow the powervalve cleaning cycle to occur, and turn the ignition off when it's fully open, then disconnect the powervalve. This will leave it in the fully open position. You'll notice a large drop in performance at the lower RPMs, but the bike should come alive at 6K rpm and red line hard.

If this is not the case, then it's likely the reedswitch is a problem.

All of this assumes that the engine is in a healthy state. And that the ignition system is all up to scratch.

Obviously there are a multitude of factors that cause loss of performance, but assuming that the engine is good condition, that's where I'd start.

[facundo duarte]

Thanks for the suggestions @Calum . Today I checked the battery connection again, I disconnected it, cleaned it with wd40, plugged it back in and to my surprise it is now worse, the same fault but around 8k. Will the CDI have any memory and when you disconnect the battery does it reset in a certain way? I'm going to try putting the reed switch back in its original spot, causing the limiting to work, and then removing it again. It doesn't have much science but the truth is that it drives me crazy. I haven't tried disconnecting the PV yet, I have it pending to rule it out. Although accelerating at wot and without the cover, seeing the pv pulley, it works fine.

[Calum]

There is no memory in the CDI to my knowledge.

A weak battery will cause issues with the powervalve, so will things like fault rectifier and bad stator etc.

But just wanted to start simple.

Have a look at @scrimsmustang guide on derestricting your model.

https://www.slideshare.net/slideshow/derestricting-the-yamaha-dt125-r-1988-through-to-2007-scrimsmustangs-classic-yamaha-restorations/32127545

[MadGyver]

Is the power valve correctly aligned,if it has the diamond shaped base?

[facundo duarte]

@Calum Well I have news, I tried what you told me about disconnecting the PV after its cleaning cycle, however the problem persists. On the other hand, I connected the reed switch wanting to cause the limitation to remove it again (I know it doesn't make sense but I didn't know what to try). There were no changes either, but here's the surprise, since the symptom seems to be electrical but it is also confusing with a rich mixture at high speeds, I tried unplugging the black plastic bottle that is screwed to the frame on the left side and there the following happened, as expected, when leaving, especially at low rpm, it felt thin but to my surprise at high rpm it went to the red line (I had never done that) I did around 80mph at 10k, obviously air enters in excess and it does not make the best carburetion but without that plastic piece at least it suggests that the problem is not electrical. The question is the following, for the motorcycle model it carries 25 and 240 jets. Could it be a limitation intentionally that the bike is rich in highs so as not to deliver all the power and maybe it really would take 210? It is even strange that with the reed switch plugged in its original place it has made that speed or perhaps having the 3rm20 cdi such limitation does not work. What do you think about the jet? Have you read something similar? I never understood why some models have the same top end kit, exhaust and carburetor, but they still have different jets. Sorry if I wrote too much, I was excited to see a beam of light in the problem.

[facundo duarte]

c@MadGyver Thanks for writing friend, it is the rectangular version where the pulley fits, it is well aligned and works correctly, at least as far as the pv is concerned.

[facundo duarte]

On my previous two-stroke, once the stator ignition coil went bad, when I installed a new but inferior one, the bike felt rich at high revs, so it tolerated/needed less fuel than before to run properly, although it translates to less power if the bike tolerates less gas. Something similar may be happening, although on this bike everything looks so healthy and with little use that I doubt it but I will have to check it again, maybe a ground cable? Sorry friends again for so much text and thank you for your time.

[Rallyfinnen]

Sounds like you disconnected the boost bottle on the intake? (YEIS i think Yamaha calls it)
Did you plug the hole? If so, it should not idle, but would run significantly leaner on WOT, giving more rpm if it was rich before.

[Rallyfinnen]

I mean if you did not plug the hole.
If you remove it and just plug the hole, it should not affect full throttle at all.

[facundo duarte]

@Rallyfinnen Hello friend, it is not the yeis that disconnected. What I disconnected is a black bottle that goes on the side of the frame and is screwed into it. It connects to the rubber that joins the air filter box to the carburetor, I understand that not all models have it.

[facundo duarte]

@Rallyfinnen Continuing with what was said, by giving it more air in this way the bike improved significantly. That's why I doubt and maybe a 210 plane is needed instead of 240. Maybe this is some kind of limitation? What really changes in the previous, more similar models to carry this model with larger aircraft? Or I have a weak spark at high rpm, so with a higher, leaner air ratio, the mixture reaches the rpm it should reach but probably with less power.

[SpookDog]

@facundo-duarte

Try cleaning your air filter. All you are doing is by-passing the filter and sponge element.

[Calum]

Go with what @SpookDog said. If you removed the YEIS from the Carb Boot...your carb settings should be okay (perhaps a little lean), since you're not altering the air after the carburettor, merely increasing flow over the carb. If you remove the one on the inlet manifold then yes it'll be a huge air leak, but you didn't....

So that to me sounds like poor flow through the airbox system. So remove the airbox lid and give it a good clean. Make sure the snorkel isn't obstructed etc.

[SpookDog]

@Calum

yeah, yamaha doesnt recomend cleaning the foam element with petrol, but as long as you dry it out its noy a problem. then lightly oil the foam and sqeeze out any excess in a bit or two of kitchen roll. make sure to clean the rubber 'snorkel' and any dirt/dust from the top of the airbox...
brake clutch cleaner works well too...

[facundo duarte]

@SpookDog @Calum Thanks again for the suggestions but let's go in parts, Jack said, I made sure the air filter was clean, then maybe I expressed myself wrong or it was the translator's fault, but I repeat, I didn't remove the yeis. I removed the black bottle that is bolted to the frame on the side and fits into the rubber that connects the air filter housing to the carburetor. That is, imagine the air entering in excess when opening that inlet and very little through the air filter box. The logical thing would be to think that it would work worse but it was when the bike worked better at least in wot and it did not have the damn failure despite the large excessive air intake, which makes me think that perhaps I still have an electrical fault that I have not yet detected and that would make a weak spark at high revolutions that is not powerful enough to burn the fuel in wot. I even tried with everything connected without the snorkel and although it improved it was still a little rich so imagine.

[Calum]

@facundo-duarte Yes that's correct.

On later models Yamaha fitted two YEIS bottles.

One to the inlet manifold, and then one to the carburetor boot. You've removed the one fitted to the carburetor boot.

It sounds like not enough air flow to me.

If you remove the air filter/carburetor boot altogether you can see if your problem goes away and that tells you it's the airbox.

[facundo duarte]

@Calum Oh well, I didn't know he also had the same name as the other one, good to know. On the other hand, if the motorcycle is original and not modified, why do you suggest that the problem could be in the airbox if it is in good condition? Or did I misunderstand what you mean?

[Calum]

Do you have the Snorkel fitted? Is there anything obstructing the top of the airbox?

I think this based off what you've told me. Sounds like giving it more air has resulted in night and day performance. Ergo, it's intake related.