Rave Valve operation question

[IDoSeaDoo]

Hey guys, I was just pondering how the Rave valve operates... So at low RPM, the force of the spring keeps the valve closed at all times because there is not enough exhaust pressure to overcome it. But at higher RPM, the exhaust pressure forces the valve open. During the pulsation of the exhaust pressure (between power strokes), does the valve close and prevent some of the fuel/air mix from escaping the combustion chamber, or does it happen so fast that it doesn't have enough time to travel all the way back down and just floats in the open or partially open position? Does it travel down at all between the time that the exhaust pressure is high to when it's high again? I was wondering if keeping that valve open during 5-7k rpm would be feasible, or if I'd lose a lot of intake charge.

 

[AdamXP800]

Can I ask why you are wanting/thinking about changing the operation of the raves? From my experience the set up performs very well



95 XP800!!!
Keep the 2 strokes alive!

 

[mikidymac]

I think he is just asking how the operate.

You are correct in the fact that the exhaust pressure forces them open and holds them open. The exhaust pulses are so fast that they just stay open or partially open, they do not move up and down with each exhaust pulse.

The part that is not correct is they are not an actual valve like a 4-stroke exhaust valve. They do not seal the exhaust port keeping the intake charge in the cylinder. Without getting too technical they simply change the exhaust port size and timing. On a 2 stroke the intake and exhaust timing is controlled by the ports in the cylinder in relation to their shape, size and location up or down in the bore. So the RAVE valve is changing the exhaust port size, shape and timing giving you the benefit of low rpm power and high rpm power. If it was done without the RAVE valve like the 580-720 engines it is a compromise of top and bottom rpm power.

If you want to get in further you need to look into 2 stroke engines and how the exhaust wave actually scavenges the cylinders and helps keep the intake charge in while the exhaust port is closing, this is where the expansion chamber and pipe tuning come into play.

For a simple engine concept they are very complicated.

 

[IDoSeaDoo]

I was just wondering about building an electromechanical device that operates the valve based on rpm. Raves have tended to be a sore spot for me, always leaking and wearing out prematurely. And they're expensive as hell, as you must replace all the pieces. I'm just kicking an idea around in my head. I think it would just be better to throw an ace engine in there and use the v tech to unlock to 110hp.

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[AdamXP800]

Something else must be going on here. I've never heard of someone having RAVE issue to the extent you have. I've always had them perform to spec. Yes the will eventually wear and need replacing but certainly not every season



95 XP800!!!
Keep the 2 strokes alive!

 

[DanSquires]

I was just wondering about building an electromechanical device that operates the valve based on rpm. Raves have tended to be a sore spot for me, always leaking and wearing out prematurely. And they're expensive as hell, as you must replace all the pieces. I'm just kicking an idea around in my head. I think it would just be better to throw an ace engine in there and use the v tech to unlock to 110hp.

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So you want a Yamaha PV system, basically... servo controlled.
Funny, people switch to Riva gas valves on those..

 

[Spimothy Leary]

Something else must be going on here. I've never heard of someone having RAVE issue to the extent you have. I've always had them perform to spec. Yes the will eventually wear and need replacing but certainly not every season



95 XP800!!!
Keep the 2 strokes alive!

I'm with Adam on this...

I put 220 hours on my xp before I sold it and all I did was clean them twice.

 

[IDoSeaDoo]

I bought new oem set and they're already starting to show signs of leakage... maybe it's my carbs. I've been battling a lean bog off idle for years now. I've literally done EVERYTHING there is to do. I've even replaced the plastic throttle bushings. It simply will not run with stock specs. Maybe it's affecting the raves somehow too

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[AdamXP800]

I battled one forever. Said screw it and bought a used set. Problem solved

Off idle bog that is


95 XP800!!!
Keep the 2 strokes alive!

 

[IDoSeaDoo]

Did you try going up in pilot jet size?

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[AdamXP800]

No my thoughts are that it should run correct with the stock settings



95 XP800!!!
Keep the 2 strokes alive!

 

[IDoSeaDoo]

Ya, I'm just pissed that something like a carburetor can wear out. That sort of thing is hard to accept, especially if I can't tell what wore out on it or why.

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[AdamXP800]

Sometimes you just have accept shit happens. I tried a new set and my problem was 100% fixed. Was it the carb? Who knows, but I know everything on those carbs checked out but it bogged off idle



95 XP800!!!
Keep the 2 strokes alive!

 

[AdamXP800]

For the 80$ I paid, well worth the used carbs



95 XP800!!!
Keep the 2 strokes alive!

 

[IDoSeaDoo]

Where did you get them that cheap?

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[AdamXP800]

eBay special



95 XP800!!!
Keep the 2 strokes alive!

 

[AdamXP800]

http://www.ebay.com/ulk/itm/231786244648



95 XP800!!!
Keep the 2 strokes alive!

 

[AdamXP800]

http://www.ebay.com/ulk/itm/231786240725



95 XP800!!!
Keep the 2 strokes alive!

 

[AdamXP800]

Or you could try to steal these
http://www.ebay.com/ulk/itm/191763261252



95 XP800!!!
Keep the 2 strokes alive!

 

[racerxxx]

If those carbs are truly of a jet boat they would not have a fuel pump on them. They're also missing the accel pump. So I think they're earlier than that, the other thing that will designate then as jet boat carbs (later jet boat) is the return nipple faces the mag so it doesn't come out the back side like a ski does.

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[AdamXP800]

Looks like someone snagged the first set I posted



95 XP800!!!
Keep the 2 strokes alive!

 

[IDoSeaDoo]

Oh ya, that was me right after you posted. Never seen carbs so cheap. Maybe I haven't been looking in a while. We'll see, now I can't wait for summer.

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[AdamXP800]

Good job grabbing those. Deals pop up all the time



95 XP800!!!
Keep the 2 strokes alive!

 

[AdamXP800]

Oh ya, that was me right after you posted. Never seen carbs so cheap. Maybe I haven't been looking in a while. We'll see, now I can't wait for summer.

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Just give them a good going through and let er rip!



95 XP800!!!
Keep the 2 strokes alive!

 

[Kris69]

The RAVE valves are operated by crankcase pressure and not exhaust gas pressure as far as i know (it works this way in my 2004 GTI LE RFI anyway). They change the size and exhaust port height. When closed (or lowered) the port is smaller allowing the engine low down torque and acceleration. If you open them too early the engine will bog down and may not rev up at all. When the pressure builds up (higher revs) the RAVE begins to open effectively making the exhaust port bigger thus allowing engine to produce more power!

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