Quick answer since I have a 2002 as well (DE03):
1 - Swap expansion chamber (the blobby exhaust bit) to an Athena or something. This was the big thing.
2 - Pull out the reed switch from behind the speedometer. Do not disconnect it or cut any wires, just wrap it in tape and stuff it aside. It detects when the needle gets to ca 80 km/h and cuts ignition there.

That should be it, your bike should now rev freely to 9500 rpm and do 120+ km/h.

Also: ensure that the YPVS is working as it should. Remove the round cap on the left side and turn on ignition. It should rotate back and forth a little, then settle such that the groove on top is right over the hole.

Explanation on that last bit: The YPVS switches the port timing between low revs (more torque) and high revs (more power) as the revs increase and decrease. Variable valve timing, you could say.

When you turn on the ignition it rotates back and forth (flips between low and high mode) to scrape off soot. The resting position should be over the hole because they used that hole to fixate the valve in low-revs mode (and turning off or removing the solenoid actuating it) when they restricted bikes, but I believe they stopped using that method after 1998 or something. If it does not rotate back and forth with an audible "bzzt-bzzt" when ignition turns on, your YPVS is not working and stuck in either of the modes.

As for the inlet manifold I did a thorough CFD analysis and found that you cannot improve it. Leave the plastic bottle on, it smoothens out the gas flow. The carburetor should not need anything either, it is likely a Mikuni TM28SS with a 240 µm main jet, which is perfect.

@markus-w
You told me to cut the wires and keep them apart lad. That didn't work, what i did was i cut the wires and connect them at the right time to somehow bypass the restriction.

@Hark_Ptooie

It’s a bit of a headfux isn’t it? The read switch might not be a simple magnetic on/off by the looks of it. It might set to a default mode if it the CDI doesn’t detect a continuity in the curcuit?

@Blasterguy
It would be helpful to know if it only restricts the revs in top gear, or every gear? I would try joining the wires at least once to see if there’s a change at all…

It might be easier to get an earlier CDI than a read switch…

@SpookDog I'll inspect the power valve from the exhaust port and try to post pictures later, just to be sure
The bike feels fast and has good acceleration so there's a possibility that it's just my speedometer that's screwed up LoL

1997:
Screenshot from 2023-09-04 00-57-29.jpg

Hilarious thing, but it developed a plenitude of electrical problems that I was to inept to manage, so I sold it cheap. Regrets.

@SpookDog Me on my 170 🤣 No maybe not quite that low, but that's what I've come to appreciate with the Yamaha now.

You look back 15 years ago when I first used the Athena kit and you'll see a completely different opinion from me.

But now I have my other screaming two strokes, I am happy to have a DT which doesn't need to be revved to the moon to enjoy. But oh boy I've had some good rips home from work this year on the DT 🙂

I'm sorry for my inactivity... Thanks, everyone for helping me out! I opened the power valve and removed the rubber tube that is on top of the airbox. Now the bike gets much more air and breathes as it should, it goes like a beast. THANKS, EVERYONE!!

Yeah, go through the derestriction guide.

Only when you know it’s properly deristricted can you address why you’re only getting 55-60 mph from your bike. Cause that’s not right restricted or not...

@Calum ok mate. Il speak to him about it

@Coreyp90 There's a full derestricting guide pinned to the top of this section. It covers all years and is most informative. 😉

@declan You can take them off.

Inner rotor kits. But they are not practical for the road. Kill engines and no good uphill.

But for a flat track they're fine.

@NINJA thanks

@calum ok cheers

@calum said in Derestricting 97 DT125r:

@sloanparkes Sounds like the powervalve isn't set up to me.

Ya well I've moved it back the other way... but it doesn't reg above 65000 in 5th and still sat at 60mph ish I'm so sure it's restricted...

And ya @NINJA it was right at the bottom and my toolbar on my phone was covering it saying 97 to 99 😧 cheers dude

@giorgio95 Must be first DTR with cdi on the back of the oiltank ? Wire in speedo you messed with white/black from the reed switch ? Thats linked to the cdi then ypvs servo. Sounds like it could just be a bad connection in the circuit somewhere if its kicking in when you move it.

Easiest and proper way to set the ypvs cables on the pully wheel under the cover is like this.

On the pully wheel in between the cables is a notch in the wheel, when you switch your ignition on and the ypvs spins over its cycle when it comes to a rest the notch should line up with the dot directly behind it. If it does thats it set properly just make sure the cables are tensioned up ok. Same applies if you have to adjust them to get it to line up and then your good to go.

@smudge1995 The complete guide for derestricting;

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