What is this Power Valve thing I keep reading about? Signed newbie

cfauvel

Chief Petty Officer
Joined
Aug 16, 2005
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645
QBhoy or others...can you explain the Power Valve.....not familiar with PWC so getting my feet wet in videos and forums....I saw a great 3 part video of guys replacing a piston, "jug" and moving the power valve over to the new "jug".

I just don't understand this Power Valve thingy....it seems to be restricting the exhaust somehow...and appears to be linked to some cables...please teach me..

oh is this only a Yamaha thing?

Thanks
 

eavega

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Apr 29, 2008
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1,377
Yeah, Seadoo (that's what I am familiar with) calls them RAVE valves (Rotax Adjustable Variable Exhaust), and my understanding is that it opens the exhaust port as the RPMs increase for more power. There is a little tuning you can do to them to make them smooth out some, but I can tell you the difference is noticeable when they open up. My 96 GTX 787cc motor has a smooth power band right to about 5200 RPMs where the RAVE valves open up, then it jumps to about 6000 RPM and really takes off...

-E
 

ahicks

Captain
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Sep 16, 2013
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3,957
They're a maintenance item as well. They get all gummed up and stick closed unless they're cleaned regularly, so you need to pay attention and get them on your annual "to do" list to maintain optimum performance. When stuck closed they can easily cost you a few hundred rpm.
 

cfauvel

Chief Petty Officer
Joined
Aug 16, 2005
Messages
645
They're a maintenance item as well. They get all gummed up and stick closed unless they're cleaned regularly, so you need to pay attention and get them on your annual "to do" list to maintain optimum performance. When stuck closed they can easily cost you a few hundred rpm.
I see that now....texted a dude with no reply on a unit that has issues....issues are unknown to owner...he thinks fuel pump.....from what I see of a 97 1100cc it seems the fuel pump is a diaphragm pump on each carb...right?
 

ahicks

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Sep 16, 2013
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Sorry, no specific experience with this boat. You want to have the fact it's running properly demonstrated. Unless you're willing to gamble and able to buy it at a "mechanic's special" price, I would totally discount a single word the owner has regarding what he "thinks" is wrong. When you hand over the money, it's going to be YOUR boat. It will be very difficult to hold the seller accountable when what the seller "thinks" is wrong turns out completely wrong.
 

cfauvel

Chief Petty Officer
Joined
Aug 16, 2005
Messages
645
Sorry, no specific experience with this boat. You want to have the fact it's running properly demonstrated. Unless you're willing to gamble and able to buy it at a "mechanic's special" price, I would totally discount a single word the owner has regarding what he "thinks" is wrong. When you hand over the money, it's going to be YOUR boat. It will be very difficult to hold the seller accountable when what the seller "thinks" is wrong turns out completely wrong.



Oh I agree....the price point for mech specials is attractive, especially as I am pretty savvy with motors....in the $1500 range I want the damn thing to be perfectly running ....at $500 well I don't expect much...other than that it floats and all the pieces are there.
 

QBhoy

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Mar 10, 2016
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8,286
Hi
Just picked this up...probably well explained by now.
Basically an old 2 stroke trick which involves opening or closing the exhaust porting depending on power demand.
Full throttle means a mechanical/electrical servo pulls a metal spade shape device to allow a larger exhaust exit.
Less throttle means they are closed reducing the exhaust flow but also meaning the engine can accelerate quicker
As mentioned. Also called rave valves on seadoo.
They should be cleaned to remove sludge and carbon build up from the oil not burnt. On some Yamaha this means removing the exhaust manifold (bad design). Seadoo rave valves are easier accessed
Yamaha engines have ha horrible habit of dropping he power valves into the cylinder and causing enevitable damage. A few schools of thinking on this. One is that the small bar that holds them breaks and allows this. The other is that the shaft breaks itself and allows this.
Wave eater clips helps with the first theory.
A well experienced Yamaha guy over here insisted on grinding a tiny bit off the edge of mine to give a bit more clearance from the piston, should this happen.
 

QBhoy

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Mar 10, 2016
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Also very important...if you are messing with the top end and ever have them disconnected or removed...need to make sure you set them up right. They need to be in a certain position. There is a lock off mechanism when removing or anything similar. Also make sure there is no play or slack in the cables. Referring to Yamaha PVS system at least. Any slack could cause a pretty bad failure or at least poor running.
 
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