Will-
you might want to check on the yamahas version the YPVS (i think) I had a RZ350 that had one of those and you could hear it when you switched the key.  Its the same motor that is used in the popular banshees so I think you might be able to find a coulple of those around in parts to get a peek on the inside.

As far as operation I heard a bunch of different theroies, so I dont want to confuse you anymore then you might be.  I am still riding the tuning bars with my R1, but long for the buzzing bees of a two stroke.  I would be interested if you found information out pertaining to this.

Alex

Thanks Dringo,
I have a pair of barrels for an RG 250 and I see that he valves actually open up a chamber situated in the head (to enlarge the volume of the chamber at low RPM??).
I hear that the modern ones also effectively change the exhaust port timing, but I haven't seen any of these yet.

When I stopped riding bikes about 25 years ago, the power valves were just beginning to appear, and I didn't keep up with two stroke development, - now I hear that there is a very real chance of two strokes being banned, that's too bad, instead of just a blanket ban on two strokes, maybe they could ban all high polluting engines, then the two stroke could still stand a chance of being developed even further, making use of it's better qualities, and overcoming its percieved pollution problems.

Some of the later designs used a 3 blade system to mimmmick the top of the exhaust port moving. Also honda experimented with water injection into the expansion chamber to change temp & gas speed, don't know results of how it went. Ito used to plant the thing into the weeds all the time before he finished a race.
Regards,
MB

Looks like we are getting some response at last!

So what actuates the valve? I know that the particular type on my Suzuki barrels is operated by cables, but what sort of mechanism actually provides the power? and what instructs it to move, - is it normally some sort of mechanical arrangement?
I did see somewhere a while ago that in some cases stepper motors were used, but there still needs to be something which tells them when to operate - an electronic sensor/controller perhaps?

Anyone else out there who has worked with these, or know where I can get any detailed info on them?

Thanks for the replies so far.

Mine on the RZ sounded like a servo with cables.  It only did it when I switched the key on.  

On my R1 this valve system is right before it breaks off into two underneath the seat.  You cant hear it though, I hear if you go with another exh sys on these bike you have to toss the power valves.

I know quite a bit of people who are old school mechanics on bikes, some with two stroke experience.  I will ask them.

They will never get rid of two strokes all together, I dont think.  I read that 10% of the worlds pollution comes from two stroke lawn care equipment.  If true that means there is a whole butt load of them out there, converting that many people and products, wheww....mind boggling

The variable intake and exhaust tuning is trick, I learned about that reading up on turbos.  Very awesome.

Alex

Valves are usually driven by a stepper motor/solenoid via cables to the valves, usually open & close in stages detemined by the ecu/cdi. Also some of the latest 1000cc 4 strokes have a butterfly valve in the collector pipe. This sems to be in the aid of a more linear throttle responce & probably some noise issues. The honda has a cast section where it routes the gasses from cyl 1&4 through the collector for cyl's 2&3 at low - mid rpm. Similar to the RZ power valve, a rotary cylinder with a cutout, however it does not just restrict flow it deflects it as well.
Regards,
MB

Hi Dunno,
As far as I know, the RG250 used the same mechanism as the RG125. This required a resonant chamber cast into the cylinder head directly above each exhaust tract. A simple plug valve was fitted between a hole in the roof of the exhaust tract and a hole in the floor of the resonant chamber.
At low rpm the plug valve was held in the open position, effectively lengthening the exhuast system and lowering its resonant frequency. At high rpm (typically 9000 rpm) the plug valve was rotated 90 degree into the closed position.
The plug valve was indeed actuated by a stepper motor and cable linkage. In the UK the RG125 was sold with no plug valve and no stepper motor to 'restrict' them to 12bhp. To remove the restriction, most people cut a length of copper household plumbing tube and hammered it into the hole where the plug valve should have been.

Early '80s Yamahas had a very slightly more sophisticated system. The power-valve DID change the exhaust port timing by adjusting the effective height of the top of the exhaust port.
This was achieved by having a gate valve shaped in profile like the 'sector' of a circle. This could rotate through about 20 degrees and alter the height of the port.
I say only slightly more sophisticated because until the TZR series of road bikes the movement of the valve was still either 'on' or 'off' at about 9000 rpm.
Later bikes were able to vary the position continuously with respect to throttle postion and engine speed.

Kawasaki and Honda had other variations on the theme.
What you have to remember is that Yamaha were first to patent their system, which has the simplest implementation of theory into practice. The other big three Japanese manufacturers then had to find ways around the Yamaha patent, which in most cases are less than optimal.

ZR

Thanks for the detailed info everyone, though I still haven't found any really good info (with drawings etc.) on the net.
ZEDRIDER,
In the more modern versions,is the resonant chamber still used, (as well as port timing variations?)

I believe I'm right in saying that the last Suzuki RGV250 (and Aprillia RS250, which used the Suzuki engine) had power valves virtually the same as the Yamaha patent. I suppose the patent had expired by then since I guess it was first obtained in the late 1970s.
I can't say for sure because I've not cracked the cases on either bike.
There must surely be some more info out there on the web for you to find.

ZR

I have a KTM enduro bike and it has by far the most complicated powervalve setup I have ever seen. It has a flap that restricts the exhaust port opening at various rpm's. It also has a cylindrical port's on either side of the exhaust (withing the barrel) that open and close as the flap goes up and down. This is all driven by an actuating arm that is driven by another arm which is powered by a centrifuge, driven by the clutch.

I've had a few Suzuki RM's and RMX's and they are all powered in the same way, from the clutch, but the method of closing off the exhaust ports are all different.  

I had an RD350F2 for a few years.  At key-on, the valve did a full cycle to clean off any muck & debris.  Below 7000 rev/min the valve was in the normal position.  Between 7000 rev/min and 7500 rev/min the valve rotated to change the exhaust port height.  Then at about 9500 rev/min (or maybe 10000) it reverted, effectively rev-limitting the bike.

The valve was cable operated, using an electric motor according to engine speed.  A real weak link too.  Most power valves coked up and got stuck.  Even spraying WD40 (a.k.a. liquid engineering) into them didn't really work.  The only solution was a regular clean-out - normally at each engine seizure (mine seized twice in the few years I had it!).

Here's a picture of the YPVS controller:

http://erekiteru.ld.infoseek.co.jp/bike/mente/DT125_piston/YPVS2.jpg

WD40 is the worst thing to put into any rotating part. It is a water dispersant only. It dries & crystalises buggering whatever you sprayed it into. Prob did more damage to your power valve than helped. Silicon grease is the go.
Regards,
MB

Carb cleaner is my preferred choice for cleaning power valves. Spray it on and watch all the black carbon crap wash away. Don't breathe while you are doing it tho.

The banshee doesn't use a powervalve, so theres no point looking at one of those. However the remainder of the engine is practically identical.

The rgv250 uses a blade type powervalve (nothing like the RZ's YPVS system) and I believe the earlier ones used a 2 blade system, with the newer ones using a 3 blade system. They had big problems with the pins holding them together wearing out and breaking (dropping powervalves into cylinders)

There are also disc type exhaust valves (which I think are used on the rg500 and rd500) and kawasaki has one known as the KIPS system (which I think has a type of disc valve).
There are other types of valve that involve a secondary exhaust chamber.
There are another kind of valve (pretty sure it's a blade valve) used on a product known as the cheetah stroker kits (for banshees) that use some kind of system triggered by exhaust pressure.

John Robinsons "Motorcycle Tuning : Two Stroke" has some good information on exhaust valves.
 

Power valves,OK.Power valves are not really as the name implies powered at all.They are very broad in design and actuation but serve the same basic purpose and principals.By altering the timing of any of the many variables such as charge induction start,charge duration,charge induction close,transfer ports and openings and closings and duration,piston port timing and durations and piston port opennings and closings and duration,exhaust ports openning,durations and closings,the list is very big at what you can change on a two cycle engine and it is all timing relative to the degree of crankcase revolution.They will change the aspects of torque,power,boost,reliability,fuel consumption,starting,engine tempreture etc.Simply they use a valve whether a sliding flat full floating design or a rotating cam or whatever to alter the exhaust timing and change the characteristics and increase the torque of a two cycle at low to mid engine ranges which cannot benefit from the supercharging effect of the rapid sound resonating and forcing exhaust out and with that and volume,angle,length of the design of the expansion chambers which sucks the following exhaust gas out even quicker at high engine revs and the vacuum effect continuing back to the charge gas through the engine.The concept of port altering is not new,but to have a variable port timing is better than having an engine that`s good down low and mid range but lacks top end or any other fixed parameter that was the ways of old.You can have your engine tuned for top end and still have great low engine speed pull.But there are tricks that I am not sure would work on new power valve equipped engines.The one great performance booster was crank packing and I am really not keen to see a power valve engine on a high compression charge with any moving or loose parts taking the brunt of the high waste volume and pressure,I don`t know how long it would last at full boost.Other things over the years have tried to harness the many variable aspects of the many ports and configurations and most worked well.I have both raced and commuted on these dry sump mosquitoes and I love the set up parameters that you can change

A closed exhaust power valve simply lengthens the effective stroke.
 
2-strokes are amazing. We used to make the intake port so big it openened up to above the piston near BDC. Some of the charge shot right across the top and some stayed in the cylinder. Good for cleaning and charging. This all happened while the intake port would normally be closed. Overall it made a greater and more constant air flow through the carb. Another trick was moving the "points" plate with a little lever. Retard the timing at high RPM and the top end goes wild.

I own a DT 125 R 1998 (i live on a small island it is all you need over here) it has a servo and power valve but it wont open any ideas what i can try. it is run by cables if that is any help??