powervalve question (dtr) help

[jim-cr 250]

hello,currently my 1994 dtr 125 has the powervalve set to fully open all the time and is starting to get a bit annoying because the bike takes a while before actually hitting powerband and when it isnt in powerband it is very slow,but when it is its quite quick.
so the question is how do i turn it down and is it easy and how far should i turn it down?,i dont know much about power bands so any would be very appreciated. thanks

[Jebus]

Hiya, First off i got the same bike but my bike is the first model that came with the powervalve working, i.e it is fitted with the servo motor and mine is a 98 model, all previous models had the powervalve fitted but it was just sat there left open so it was of no use for what the thing was designed for.

It really amazes me that people do this yamaha spent a lot of time effort and money designing the powervalve and them people jam them open thinking thats better. The power valve restricts the flow at lower revs and this helps the bike produce a bit more power and smooths out the power at lower revs and after 7kish revs when it opens up it stops restricting the flow and then the bike can breath fully because after these revs the engine doesnt need the gas flow to be slowed down it all sorts its self out. Sorry i dont really know vast amounts about the little gizmo but a few guys on here will give up more information, most of what i got above should cover what you need to know about the valve

First it will depend on what year your dt is but you will need the servo motor and cables to connect the motor to the powervalve and other stuff as well i would imagine and then its setting it up as per haynes manual.

The "powerband" is a term that applies to the "band" of revs that produce the power on a engine, and most 2 strokes have a very narrow band in which this happens and it normally is quite a jump from the power produced outside of the band, this is what makes 2 stroke engines "peaky".
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2nd time around CBT: 8/9/11
125 Varadero

[KatOwner]

The Powervalve is actually a piece of automotive brilliance ( in my opinion anyway! )

In a 2-stroke, the exhaust port is one of the key measures on a tuned engine. The sooner it opens on the down stroke, the sooner the engine can pump fresh mixture up from the cases into the cylinder, and the better the scavenging will be. This gives more power. Home tuners used to get out the files and do this for themselves to squeeze out a bit more power. The flipside was, of course, when the engine was spinning slower, instead of getting a good charge of mixture in teh cylinder head and blowing all the burnt stuff out, you ended up blowing a lot down the pipe too. This LOST you power. The term 'powerband' refers to teh fact that tuning squashed the power up into a tight rev-range. Usually at the upper rev range. Great if you are racing.....

So....have the exhaust port open later and you get good low end power and traction. Earlier and you get top end performance but loose a lot at low revs.

Power valve means you get BOTH. It's a simple valve that varies the effective time the exhaust port opens. Brilliant! They copyrighted it and forced all the other manufacturers to mess around with resonance chambers and such until the patent expired...then they all just copied Yamaha!

If you can track down the servos, cable etc. and get a fully functional powervalve you will get a lot more midrange, lose the sharp powerband and STILL have the same top end performance you have now. Shutting the valve will give you the midrange but will strangle top end power.