YPVS Valve not moving when at high revs

YPVSdreamer · L Plate Warrior Joined: 13 Jun 2026 Karma :

Hi all,
my 1991 F2 model had just developed a new fault and lost midrange power. The power valve does not move when the bike is revved up to, and held at, 7000 rpm. The valve does the clean sweep when the igition is turned on, returning the valve pulley to the reference point. When the engine starts up nothing else happens. The cables are the correct way round.
The bike pulls hard and fast as soon as I get over 7500rpm, suggesting the valves are stuck in the open position.

Questions:-

As i understand it, the initial reference setting point (holes aligned), corresponds to the valves in the full open position. Is this correct? The exhausts are on with new gaskets and I am reluctant to remove them just to check.

Should the valve move to a closed position when the engine fires, so that low-speed running enjoys a closed exhaust port?

Does the valve move clockwise as the revs rise? To my mind, this seems opposite to the logic, unless the valve should move clockwise, to the closed position when the engine starts running, and then anti-clockwise once the revs rise. Can anyone explain the sequence, please.

Also, what does the group think the fault would be? Lack of signal from the CDI module?

Any help would be greatly appreciated. The summer is here and my bike is in the garage.
Cheers

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

It's been a minute...

When I had one of these, the issue I thought was a dodgy YPVS valve was actually a bad earth that I solved with a pattern wiring loom. The symptoms weren't exactly the same though. Mine would open, it's just it would open when it decided to, not when I decided to, which meant the bike was like a bucking bronco to ride.

Have you removed and decoked the valve? Does it move smoothly? Have the YPVS cables become stuck or swapped maybe?

I can find a workshop manual on the internet quite easily but it's in French for some reason.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

https://davestestsandarticles.weebly.com/uploads/4/8/4/5/4845046/yamahard350_fii_nii_ypvsmanualen.pdf

Try that, page 146 I believe.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

YPVSdreamer · L Plate Warrior Joined: 13 Jun 2026 Karma :

Thank you MarJay. I will check that out.

The cables are definitely the right way round, and the valves are clean able to move freely when the cables are slacked off.

I'm tending toward a poor or missing signal from the CDI unit. Not sure how to test this though.

Does anyone know how to do that? I have a multimeter, and that's about it.

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

YPVSdreamer · L Plate Warrior Joined: 13 Jun 2026 Karma :

So, an update.

I have figured out that the CDI feeds the same signal to the tacho and the YPVS control unit. The tacho is working just fine, and the grey line between the tacho and the YPVS is connected (becomes yellow and black at the YPVS controller end).

All other electronics are working just fine.

I think I have to conclude that there is a fault with the YPVS controller circuit board. Perhaps one of the components has given up after 35 years. This would not be too surprising, I guess.

The valve does the initial bizz buzz at start up, but no movement as the engine builds revs.

Does anyone know of a good replacement system for the PV controller?

MarJay · But it's British! Joined: 15 Sep 2003 Karma :

Zeeltronic is the one everyone uses and it's REALLY good, but it does ideally need setting up to get the best from it. I think the defaults tend to be pretty decent though.
We are very lucky to have access to a quality replica of such a niche item, the people who make it are bona fide geniuses.

However, lots of people are quick to jump to the conclusion you've made about the PV controller. If it cycles OK on start up, then I can't see how it would fail at other times, but I can see how a wiring or earth connection could break down at temperature (i.e. when the engine is hot). You can go for a Zeeltronic, and it may well fix the problem but I'd ONLY be doing that if I had a surfeit of cash and a deficit of time to be honest. The Zeeltronic is cool, and when set up properly you can get a bit more out of even a stock YPVS engine with it but they aren't cheap.

https://www.zeeltronic.com/page/yamaha.php

https://www.mb-designs.co.uk/webshop/road-and-road-racing-bike-specific/yamaha-rd250lc-350lc-350ypvs/ignition/zeeeltronic-pcdi-10vt/
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.