power valve mod for 1998 yz 250

[yzJoKeR]

I was talking to a guy who has the same year yz as mine he had a shallow plate on the left side power valve instead of the factory cover which is about two inches in depth. he said it was a factory yamaha mod that changes the air volume around the valve and help with mid range. Does anyone know if this is true because it wouldn't be too hard to make that style plate.
Thanks in advance
JoKeR

 

[yz250roost]

actually I heard that it did make a difference, in 98 almost all the pro's ran those covers and they were actually not very pretty (probably not for "cosmetic" purposes. I figure that one day I'll make one for my bike but I just havn't gotten around to it, and yes the principle is that the volume of that chamber is decreased and somehow that changes some characteristic of the power. I wish Eric Gorr could see this and maybe shed some light on this topic that has been discussed before. Why not just make one since it is very easy looking and let us know if you do, I'm very curious,
Jeff

 

[yzJoKeR]

I will do that, if it does i'll let you know and try to make you one also, we have a great machine shop at work. I'm just glad someone else heard about it the guy said the same thing that only factory guys knew about it. ;)
Mike

 

[Lorin]

Actually, I would like to see one of those as well. I have the same bike and am curious as to the benefits. Seems as though lately, most mods to the powervalve cover involve creating more space and volume, not less; in hopes of making more bottom end. I would like one of those covers as well if you make up a batch. PM me if you end up doing some.

 

[yzJoKeR]

my buds in the machine shop made my plate it looks sweet they even stamped yamaha on it lol. I'm going rideing this weekend so I'll let you know how it goes. I also was talking to a guy at work about it he said any time you can raise the secondary compression that it would help. So I guess we will see.
JoKa

 

[Rcannon]

Yes, please let us know how the plate works. I have thought about making a test plate. You could use the stock plate, but make an intermnal cover of filler to reduce the volume. I am curious as to what it might do for the low end, if anything!

 

[whyzee]

Rcannon, that's a good idea. I would think using a filler to reduce volume inside the cover would work best, while still providing a good seal. Would you think JB-weld would work?

Joker, looking forward to your conclusions as well.

 

[MikeT]

How about some high temp silicone? Clean it out with brake cleaner, then fill it up, if you like it, keep it in. If it doesn't work, pull it out. ;)

 

[bclapham]

how much is a spare cover if it doesnt work? i dont like the idea of putting "temporary" items inside an engine. I bet JB would work, and there are also a lot of epoxy's that would also...i saw a thread not long ago.

 

[Rcannon]

Honestly, we could probably run a test with some aluminum foil. Ball it up and put it in the cover... I will try it this weekend.

I saw a company selling flat covers for around 25.00. I e mailed them, but they did not respond.

I did notice that Tim Ferries 1998 YZ 250 had the stock cover on it.

 

[yzJoKeR]

hey RC can you post a link to that pic if you have a chance. :thumb:
Thanks
JoKeR

 

[Rcannon]

Here is the link to the shop that sells the covers. I wonder if a carbon fiber plate would hold up?

http://www.surfnturfracing.com/customyz.htm

 

[Rcannon]

I should ahve mentioned this. I dont know anything about this shop. I do know that they do not bother to answer e mail....

 

[yzJoKeR]

Went rideing today, oh ya first, my bike is a 98 yz250 with procircuit pipe and silencer,delta2 reed block every thing else is stock and my new plate I got some pics of it I'll post them tomorrow. WOW it pulls much longer and has much more throttle response than before the mid range hit is much smoother than bfore.When turning I use the clutch alot but now the power comes on much sooner.The plate deffinetly makes a diffrence and well worth getting someone to make you one. hope this helps
JoKeR

 

[yzJoKeR]

Here is a pic of the cover it's 3/16 alum http://TheDoGG.clanpages.com/cover.jpg

 

[Rcannon]

Is the low end different than before?

 

[yzJoKeR]

not too much but it does have a little more bottom end.

 

[MikeT]

Originally posted by bclapham
how much is a spare cover if it doesnt work? i dont like the idea of putting "temporary" items inside an engine.

I really doubt you would have any problems with the high temp silicone, plus pulling it out won't cause any damage. New part, $25+ bucks, silicone $3......

 

[whyzee]

Joker,
Nice pic and nice clean job.

 

[Rcannon]

I built one today using some 1/8 aluminum , my jigsaw, and my Makita drill. It was not very difficult. I took my stock cover and made a copy of it in the copy machine at work, then glued the pattern on the aluminum.

Trying it in front of the house, I would say midrange is up a lot. At least as much difference as my Rad Valve made, maybe more. Low end feels similar, but not less.

This is a good, cheap mod.