Yamaha DT 125R 2002 performance after 14 years of ownership

[Andetover]

I notice there is still a lot of interest in the good old DT125R, and how to derestrict them.
I'm a middle aged biker with over 35 years riding experience, I've owned several hot 2 strokes, and my favourite is my little DT.
I enjoy it more than my GSX-R!

My DT is a 2002 model on a "03" plate. I bought it in 2004 off the original owner with just 1,100 miles on the clock, it now has 5,800 miles.

Everything is standard on it, I use fully synthetic oil, and always warm it up carefully before thraping.
When I first had it, it would wheelie ok, but ran out of puff at about 65mph. As it got older the engine loosened up, and at 4,000 miles I had new piston rings fitted... the engine was coming apart anyway because of a gearbox issue, and it's always a good idea to check the rings and top end bearings if it's apart.

Currently, on a a good day, when the atmospheric conditions are right (big factor in any engine not fuel injected), it nearly revs out in top, the speedo needle hitting the stop at 80mph, and a GPS verified top speed of 82. That's on standard gearing, standard exhaust etc.

The only things to note are I moved the reed switch and wrapped it in electrical tape to protect it.
If you shake the front section of the exhaust you can hear a rattle... presumably at least one of the welded restrictions in the pipe has separated and freed up the header pipe.
When I put in a new, genuine Yamaha replacement air filter I felt an immediate increase in response.

And I had it tested on a dyno. She is putting out a peak power of 17.2 bhp.
The torque curve is all over the place, but they checked out the emissions and assured me that at full throttle the mixture is safely rich.

So no need to change pipes, or mess with the airbox. On the later models you have a working power valve, and I would love to fit a zeeltronic kit and adjust when it kicks in to give better torque, but in all honesty, if it's well maintained and not abused, you can have loads of fun on, and off road.

Just wanted to dispel any myths.

[Meatybeaty]

Good write up matey, any Pictures

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I have a mate who brings loads of DTR/TDR 125's and other 2T bikes over from France to sell over here (Unit 5 Motos/Stinkwheels). There's quite a demand for them over here at the moment.

If the OP doesn't mind losing a bit of torque, you can peg the power valve permanently open. You get a bit of a hole mid range, but will add a fair bit to the top-end.
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[Andetover]

It's not allowing me to add a photo of the dyno graph!

[stevo as b4]

I'd like to see you run it on the same dyno but with a 1989 DT125R CDI box instead, as from what I hear the later DTR's are very strangled electronically.

My sick, badly re-jetted, badly sleeved KMX wouldn't crack 19bhp on its first dyno run, and if it was perfect and standard I'd have expected a bit more if I'm honest.
I still wouldn't have left it standard though, but Im really wishing I'd bought a 125 that I wouldn't have dared to modify from standard spec.

[Andetover]

I never owned a KMX, but back in the late 80s a mate at work had one, I had a Suzuki TS125X and later on we both had TDRs... but that's another story.

You could derestrict the KMX by cutting a grey wire under the seat, and allegedly getting 21bhp... but the power valves were supposed to be a weak point, and I have to say that compared to the DT, my seat of the pants dyno found the KMX lacking in low down torque.

The TS used to bomb up to an indicated 80 on a good day, but I don't think that was genuine. I took the original airbox off, stuck a cone filter on, upped the main jet and fitted an oval silencer on the back. It was pretty gutless below 6,000 rpm, but then hit the power band hard.
On one memorable day I was off roading in the fields behind Rookery Hall Hotel in Nantwich and broke off the front brake lever AND the clutch lever.
Then had to ride I to Crewe for spares... at the lights I had to rev the tits off it, slam it (with no clutch) into 1st, control the wheelie, and snick up into 2nd before I flipped it, or stalled it if there was traffic... and at one junction, I had to do all that whilst turning right!

A little old lady told may mate "He's mad he is!"

They don't teach you to ride like that any more...