Power Valves?

[Henriettaah]

Not sure where this should be..!

Seems the RD might have a power valve fitted. Rev the engine and when it hits about 7k it screams! Don't know much about these. I know that

...the biggest change came with the introduction of the Yamaha Power Valve System (YPVS) Unfortunately for us Brits, the Servo motor and cables to operate the Power Valve was omitted for 12bhp laws. Servo kits were available to buy if you wanted to fully unrestrict it. Though most people would just manually turn the powervalve fully open

Where is the power valve? What does it look like? Could manually turning it fully open affect the running of the engine?

I ask because there's something afoot with the carb - when revving the engine for a gear change, its unable to get above about 4k or something terrible like that. So going uphill is an awful struggle. Hit the flat and it can recover somewhat, but is still not right. When riding it, you're unable to hit enough revs to get the powervalve to kick in anyway.

Any ideas? Its going for its MOT today and should get through but there is still this carb problem to deal with before its rideable.. anything to do with the carb needles..?

[Mintbread]

Is it blowing much smoke after it has warmed up?
I had an '85 RZ(RD)500 with the YPVS and it was a scream to ride but horribly temperamental. The power valves are designed to open more at higher revs thus giving the bike more power. That surge at 7k sounds like the two stroke power band. My bike used to hit it at 6.5k and shoot up to 10k in the blink of an eye, trying to suck me off the back as it did so.

Check and make sure the plugs aren't fouling due to excess oil. I had my oil pump adjusted after I went through four sets of plugs only to find out the plug caps were shot.

Unfortunately there are so many possibles as to why a two stroke won't run well. Try giving it an absolute hiding on some back roads as they like to be ridden hard and it might clear things out.

PS: I am in no way considered mechainically inclined but from experience they can be a pain to keep running well.

[Henriettaah]

When it had been warmed up and ridden a mile or so it was hardly smoking at all. I'd say normal for a two stroke - some smoke, but minimal - especially compared to when it was cold!

Yes, the spark is oiling up - wondering if the autolube pump needs adjusting - but that involves fiddling with washers and stuff...

Shall have to pick the brains of the tester guy at the garage and see what he can suggest too.

[storysunfolding]

Not sure about your specific bike but when my main jet in the carb gets gunked, it won't give me much power about 4k.

[mysta2]

I left these all full size and tweaked the levels in hopes that you could actually read them:







all out of last months Classic Bike

[Henriettaah]

*lol* excellent post there!

On examining the bike, I don't think there is a powervalve fitted - where it should be, it isn't. Is this the only kind of power valve that could be fitted? If it is, then the screaming at 7k must be standard for the mark II.

When a bike is 'restricted' and 'unrestricted', what is it that does this? Restricts, I mean? And what exactly is restricted? Is it the acceleration or the top speed?

[BuzZz]

If your bike is a restricted one, the valve itself will still be in the cylinder as it forms part of the cylinder wall itself. But the actuation devices, the cables and small motor that opens and closes the valve is not installed.

It sounds more like your carbs need adjusting or jetting. I would try dropping the needle one notch at a time until it runs right. That means raising the clip that fits into those notches, lowering the opposite end of the needle in the main jet and leaning the air/fuel mixture.

It is unlikely it is due to the injection rate of the 2-stroke oil. More oil takes up volume in the intake tract that would otherwise be filled by gasoline, causeing a lean mixture.

[Henriettaah]

The bike passed its MOT yesterday, but the carb needs taken off and the jets cleaned. Another learning curve today!