YZ powervalve cover

[yz250roost]

I have a 98 Yz 250 and have found an aftermarket powervalve cover for it. The cover is said to improve low to mid power. My question is how does it do that? It's just a little cover to drain the powervalve residual oil out of. Does anyone else have one of these and would like to give a response? thanks in advance,
Jeff

 

[Rcannon]

Where did you find the cover? I would love to see one. On these bikes there really is two covers. The outside beauty cover and a real cover inside. I wonder if the inside cover is what they sell? I imagine playing with the stopping point of the powervalve might change the powerband.

 

[yz250roost]

yeah I actually just got through replacing the inside cover, but the outside cover is the one that I have the opportunity to buy from surf and turf mx, do a search and it'll come up. I havn't been able to find anyone else that sells them, maybe boyesen? I really have no idea what the significance of the outer cover plays in the performance of the bike. The stopping point on those inside covers is what drove me to buy a new one, in Mr. gorr's book he says after .03" you should replace the innner stop plate because of a chance that the piston could hit the powervalve. I took mine apart and had to replace the powervalve and the stop itself,
Jeff

 

[Rcannon]

I remember you posting about this before. How could that outside cover do anything? I just do not understand. Inside the cover looks just like the 94 yz's.

I am curious enough to call them...

 

[yz250roost]

I know, I was hoping someone around here had put one on, When I look at back issues of MX action and Dirt rider I see that the pro's run them on their bikes, I just don't understand, the only thing I can think is that if you look towards the front of the bike with the cover off, I think that I can see that it ties in with the end of the exhaust port and that if you took at stick you could actually stick it into the exhaust port, this means that the expansion area in that cover must play some role, so I am taking a guess that the flat cover that is put on in replace of the bulging cover reduces that area inside that cover and somehow produces more power, that's my guess at it.

 

[Rcannon]

I like your guess. The area is vented. reducing this could change something...I think I will order one on payday. It sounds interesting.

 

[yz250roost]

let me know if you do, I'd love to see a review on one of these, and if I get that one I'll do the same,
Jeff

 

[CanadianRidr]

Im not sure but does it have the same priciple that there is more volume just like the CR powervalve spacer?

 

[Rcannon]

I think I figured this out. Eric's book says the 97 and 98 do have a renisance chamber (spelled wrong). The 94 does not. My guess is this. The chamber has a certain volume. The flat cover has less volume than stock. I imagine it acting like a shorter headpipe to boost midrange and topend.

I love the low-end my bike is making. I would not be willing to give this up. A person could make an extra cover to fit under the stock one to test this. For me, the bike is powerful enough in the midrange. I could not afford the underware bill if I added more.

 

[yz250roost]

hahah, good one RCannon