Roost King

Member
Jan 13, 2001
29
0
Ok, i noticed my bike was losing the ability to rev fully so I pulled it apart. What I found shocked me. The powervalve actuating rod had come loose from the valve lever. The plastic clip had come loose and... it gets better still; the lower clip had also come loose and the rod was damaged. There was no powervalve governor damage, thankfully, and everything else was fine. I ordered the parts today and they will be in next week. And a week seems like an eternity to go without riding.

So is it alright to continue riding without the powervalve functioning? I know it will hurt the performance of the bike, but will it also cause any bad things to happen to my engine? Im thinking about just removing the rod and riding with the valve closed.
 

cr125_king

Member
Apr 2, 2001
343
0
Just wait a week for the parts

why would you put your bike back together without your power valves working and then go riding?:think . Cant you wait a week for the parts?. I not an expert on P.valves but your bike wont run good without them working (i dont think you'll have a powerband>flat power range). I wouldn't do it though. Just wait:cool:
 
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RM_guy

Moderator
Damn Yankees
LIFETIME SPONSOR
Nov 21, 2000
6,943
174
North East USA
You can ride it but you won’t have any top end power. It sounds like you were riding it that way anyway. You will notice a BIG improvement with the PV hooked up.
 

spanky250

Mod Ban
Dec 10, 2000
1,490
1
I had something like this happen. The arm was damaged, so it would stick either open or closed. I rode the rest of the day like that. At first i pushed the valve rod closed, but the power was so reduced I couldn't get up easy hils. Then I puled the rod to the open position, with the valve stuck open, it was like riding a big,hard-hitting 125, with no bottom and a huge hit in the mid. It definitely made the ride exciting.;) It was hard to get moving on hills and slick spots, but lots of clutch abuse got me through the ride. I definitely fixed it before riding again.;)
 

jadair

Member
Dec 10, 2000
21
0
p valve

It wouldnt hurt to run it like that the only thing you will lose is low end if you leave it open if you leave it closed the motor wont rev out like it could the power vavle just restricts the exhaust at low rpm. it wont hurt the bike.
 

spanky250

Mod Ban
Dec 10, 2000
1,490
1
Re: p valve

Originally posted by jadair
the power vavle just restricts the exhaust at low rpm.
The powervalve does not restrict the exhaust. It changes the exhaust port timing. When the valve is in the closed position, it lowers the top of the exhaust port, making the port open later in the stroke. This effectively moves the torque peak down in the rev range. When the valve is open, it raises the top of the exhaust port, allowing it to open sooner in the stroke, moving the torque peak higher in the rev range. Some engines do have small sub-exhaust-ports that the valve assembly uncovers when open to allow more flow at high rpms.
 

motopuffs

Member
Mar 15, 2001
182
0
although the primary method of tuning here is via changing the port timing like you say spanky, at low rpms the exhaust is restricted, since the port opening is smaller.
 

spanky250

Mod Ban
Dec 10, 2000
1,490
1
Originally posted by motopuffs
although the primary method of tuning here is via changing the port timing like you say spanky, at low rpms the exhaust is restricted, since the port opening is smaller.
Low rpms require a smaller exhaust port to keep the exhaust velocity up to enhance the scavenging. I look at a restriction as something that slows down the flow.
 

jadair

Member
Dec 10, 2000
21
0
p valve

Being restrictive is just about the same thing as changing the port timing. I allready know this you dont need to try to correct me.
 

motopuffs

Member
Mar 15, 2001
182
0
so in other words the bottom line is slightly less voume per time unit, but more overall volume is scavenged due to greater momentum of the gasses.

if we really studied it, I think we would find it's still a restriction, technically, but a good trade off. Not worth debating tho, really.
 

motopuffs

Member
Mar 15, 2001
182
0
I had an RM250 overbored to 300, of course the powervalve had to be modified, and it wasn't set properly the first time I rode the bike. I couldn't believe how much difference the adjustment (spring tension) made! Totally changed the personality of the engine.
 

spanky250

Mod Ban
Dec 10, 2000
1,490
1
I wish all manufacturers would give us adjustments on the powervalve like Suzuki and KTM. How hard could it be to add a simple preload adjustment?
 

WWR

Sponsoring Member
Jul 15, 2000
161
0
I believe that a mechanically controlled powervalve is soon to be a thing of the past, eliminating the "need" for a spring-tension adjustment. I cant wait to see the results of the electronincally controlled kind, and hopefully software to tune them. The ones on my NSR open at different increments for different RPM's, and make for a very smooth and linear (almost electric) powerband.
 

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