Modifying Yamahas powervalve system YPVS

Dischord · World Chat Champion Joined: 08 May 2005 Karma :

It's very difficult to tune the powervalve exactly how you want and I recall someone saying before they used to operate the powervalve via a bicycle gear changer mounted on the bars. I'm not sure if this is true to all YPVS systems but on the DT125 in stock form it doesn't open more than about 1/4 - 1/2 way when flat out.

Now this sounds like a really cool idea to me, keep the valve closed for town riding and then the second you hit the B roads / dual carriageway open the valve up for more top end grunt.

Has anyone tried anything like this before? would it even work or where they bullshitting? I think I could open the valve via a lever but having it return to the closed position is another thing entirely, would have to sort it out with a spring somehow.

Any ideas? would be interesting as you could switch from 15hp to 20+hp instantly!
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G · The Voice of Reason Joined: 02 Feb 2002 Karma :

The powervalve servo on my CRM was dodgy.

Until I got a replacement I just had the wires sticking out by the tank.
So I pulled on one if I wanted more top-end power or the other if I wanted more midrange power.

Personally, I'd look at a way of making the system work properly in the first place.

For road use, I'd go with top end over midrange all the time, if I had to choose.

An old-style racing bike gear changer would probably do the trick; reckon you could probably mount a cable each side so you've got the return as well.

Dischord · World Chat Champion Joined: 08 May 2005 Karma :

Interesting G, I didn't really consider using 2 levers - one for return! Thinking about it though that sounds like the simplest way of doing it.

My riding style varies quite a bit, I like to pull wheelies and go up the mountains so torque is pretty useful there but don't want to be left with 60MPH top-end DT125! Very Happy

I reckon I could make a custom bracket and mount the 2 levers somewhere apart from the bars, so I could use the stock cables instead of extending them?
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G · The Voice of Reason Joined: 02 Feb 2002 Karma :

I was thinking of a single one with a cable mounted the other way for the return, however you could use two too.

If you mounted them lower down you could use the original cables.

Oh and your title reads:
>>Yamahas YPVS powervalve system<<
which is
>>Yamahas Yamaha PowerValve System powervalve system<< Very Happy

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

The lever on the bars for the power valve was a cheap bodge solution. Sold because it was far cheaper than the proper power valve kit from Yamaha.

Opening the valve further is not going to make the bike quicker. Effectively all it would do is start to close again. It is a half cylinder, and in the open position the engine side of the half cylinder will be flush with the top of the exhaust port. Open it further and the back end will just start to come down into the exhaust port.

Exactly the same as if you tried to open a throttle throttle butterfly beyond fully open.

All the best

Keith
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stinkwheel · Bovine Proctologist Joined: 12 Jul 2004 Karma :

I would appreciate the subtle irony if you used an old-style ignition advance lever (as fitted to pre 1950's motorbikes) to work your powervalve. It would have a similar effect too.
https://www.vehicle-wiring-products.eu/VWP-onlinestore/motorcycle/photolevers/w83005.jpg
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firefox · World Chat Champion Joined: 20 Oct 2005 Karma :

why dont you just put an electric one on ?
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Dischord · World Chat Champion Joined: 08 May 2005 Karma :

It already has an electric one, it's just a load of crap Razz

@G - cheers for that, guess I better change it lol never knew what it stood for! Very Happy

@Stinkwheel - I think people would probably mistake that for a bell Laughing

@Kickstart - I was under the impression it was a simply a valve that controls how big the exhaust port is? If I adjusted the 2 pulleys on the servo I saw massive gains in power and speed. Just thought a bike lever would be a quicker way of adjusting it instead of getting the spanners out every 5mins?
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Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

dougon2wheels · Nitrous Nuisance Joined: 28 Feb 2006 Karma :

Dischord · World Chat Champion Joined: 08 May 2005 Karma :

That's why I wanted a quick way to open and close the powervalve - with a lever for example Razz

Like you say with the valve wide open the bike doesn't want to move unless it's over 8k or so and is almost fighting against you under that. Yet with it closed it has plenty of torque but basically no powerband at all.

Would be cool to pull off the mountain, flip a lever and have the bike ready to hit the roads without getting off and adjusting the cables!
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2012 KTM EXC 250

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