Yamaha DT 125 DERESTRICTING
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All you’re gonna have to do is undo the pulley bolt and rotate the power valve till it’s ‘smooth’ with the exhaust port and refit the pulley. It should cycle closed then open when you turn on the ignition. It should only close again when you run the engine...
Should take you 30 mins, then enjoy!!
P.S. there’s a good chance that you will have to adjust the cables as well. Just make sure that the power valve is at the open/smooth position, that the pulley pointer/thing is set towards the little 3mm hole and adjust to fit..
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By the way you have the power valve set I’m guessing you don’t really get past 7000 rpm in any gear?...
I have an early Dtr like yours. I also have a working power valve servo fitted. Finding out information on how to properly fit it was nearly impossible. I had to watch videos of 3wire servos starting up on ignition then running. I don’t know about later 5wire servos, but your power valve needs to be set in the ‘pinned open’ position when the engine isn’t running. The way it is set at the moment it is restricted and the servo will only try to close it more. It’s a wonder that it runs any sense at all the way it’s set...
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By the way you have the power valve set I’m guessing you don’t really get past 7000 rpm in any gear?...
I have an early Dtr like yours. I also have a working power valve servo fitted. Finding out information on how to properly fit it was nearly impossible. I had to watch videos of 3wire servos starting up on ignition then running. I don’t know about later 5wire servos, but your power valve needs to be set in the ‘pinned open’ position when the engine isn’t running. The way it is set at the moment it is restricted and the servo will only try to close it more. It’s a wonder that it runs any sense at all the way it’s set...
@SpookDog That's how I usually set my valve.
I've never encountered problems aligning the valve.
Going from a completely broken setup to work.
Turn ignition on and off. This is how the powervalve should be when it is fully open.
So it is just a case of adjusting the cables so that the valve is flush with the exhaust port. In some instances people have put the cables around the wrong way so that it is not operating correctly. But that's easily rectified.
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Yeah, the cables are clearly numbered 1 & 2. In my case they didn’t match up. I had to cut some outer off of one as well, to make it fit and work.
unbelievable!Getting the power valve fitted and the servo working was like one of the biggest mine-fields since the Somme
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Yeah, the cables are clearly numbered 1 & 2. In my case they didn’t match up. I had to cut some outer off of one as well, to make it fit and work.
unbelievable!Getting the power valve fitted and the servo working was like one of the biggest mine-fields since the Somme
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I sounds like a dog!
Seriously though, it sounds a bit ‘clicky’ to my ear. A bit hesitant as well maybe...
It’s really hard to tell without being there and hearing the whole range of sound frequencies...P.S. Have you done your power valve yet?...
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Does my DT sound properly?
https://youtu.be/Id1jsvah8T8 -
Any old 2litre bottle top will plug the hole...
I didn’t want to say before but does that piston look like it was partially heat seized? Those are vertical score marks, no?
Not that I haven’t run a lot worse before 🤪
Sort out the power valve and see how it runs after bud. Then worry about if the top ends rattling. It could even be too much back pressure from an over closed power valve making the piston slap??P.S. is that the side bottle, or the one that sits on top of the inlet manifold?...
My eyes aren’t as good as they once were... -
Any old 2litre bottle top will plug the hole...
I didn’t want to say before but does that piston look like it was partially heat seized? Those are vertical score marks, no?
Not that I haven’t run a lot worse before 🤪
Sort out the power valve and see how it runs after bud. Then worry about if the top ends rattling. It could even be too much back pressure from an over closed power valve making the piston slap??P.S. is that the side bottle, or the one that sits on top of the inlet manifold?...
My eyes aren’t as good as they once were... -
@SpookDog It changed sound when I tried to adjust power valve... Maybe I should try to put it in position it was before.
Where is yeis bottle supposed to be? -
@Lukas55 IF YOUR cylinder has been rebored but your pv hasn't been machined the piston will hit your pv check the piston with the exhaust off again
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@declan has to be a few rebores. You are okay on just one rebore.
If the valve is pinned open it will sound loud. Also if the rubber gaskets are knackered on the powervalve end caps it will sound gash.
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@Calum sure but it is a dt not exactly new bikes who knows how many bores it’s been through
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It’s over 57mm I think that it needs reprofiling ...
Make sure the power valve isn’t 180 degrees out. As long as it is fully open when the engine is off it’s ok. That and the cables are right. You should notice a huge increase in performance. Let us know how you get on...
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It’s over 57mm I think that it needs reprofiling ...
Make sure the power valve isn’t 180 degrees out. As long as it is fully open when the engine is off it’s ok. That and the cables are right. You should notice a huge increase in performance. Let us know how you get on...
Best way of checking the valve is open when it should be, is to rev the bike over 7k. Then turn the ignition off (while it's above 7k). Then check the position of the valve. From what I've heard on here, different years operate the cleaning cycle etc of the valve differently.
If it's revving out fine in fifth. It might just be down to a not 100% healthy engine not having the power to pull 6th gear well. -
So when it is closed (when the bike is off) it looks like this...
https://www.youtube.com/watch?v=kephUMfdNIo&ab_channel=oupzySo the sound comes on higher RPMs when the valve is open I guess... Can I adjust it with cables on the side of the cylinder so there is less chance of hitting the piston or it is only possible with the cylinder off?
BTW sorry for my bad English... -
Best way of checking the valve is open when it should be, is to rev the bike over 7k. Then turn the ignition off (while it's above 7k). Then check the position of the valve. From what I've heard on here, different years operate the cleaning cycle etc of the valve differently.
If it's revving out fine in fifth. It might just be down to a not 100% healthy engine not having the power to pull 6th gear well.
