250-500cc 2004 WR 250 with 300 big bore kit - power issue

yeah it might be, the 2c racing pipe is suppoused to make the 250 have great top end, however because of the 300 size bore it might not be doing the job.

If you are talking about the nut in first photo of your last pair of photos, it very well could be the problem. If the travel of the arm that nut holds tight is limited the PV won't open all the way.
Like you say, put it together and try it.
PS here is how to check the adjustment. The pictures that used to accompany this post have expired but I think you will get the idea.:
The PWK 38 did seem to help on my '07 WR 250 as well. The bike did seem smoother with less violent hit. As far as adjusting the power valve height, here is some information that came from either a member here or TT. I am sorry I do not remember who to give credit to. Hope this helps. If adjusting this be extra careful that the power valves are not so close as to rub the piston skirt.

1. Remove seat, gas tank, right side cover, silencer and pipe
2. Remove radiator cap and drain coolant
3. Remove upper motor mount and spark plug
4. Disconnect coolant hoses from head
5. Remove head and right PV cover
6. Move piston to bottom of stroke
7. Measure from bottom of PV to top of cylinder. See photos
8. You will need to improvise an accurate method of measuring. I made a small L-shaped plastic ruler with two marks for the settings I use. The short leg of the L needs to be just long enough to grab the edge of the PV. See photo
9. Make sure PV adjustment arm is bottomed against case when measuring. See photo.
10. Loosen bolts and adjust PV height.


I use 48.0mm for MX. It gives great top end power at the expense of bottom and mid.
I use 50.5mm for woods riding. Good grunt, but not as much peak power or revs.

Yeah that's what I was thinking! im putting it back together this afternoon. ill let you guys know how it goes. Head bolt torque is 18ft/lb yeah?

ok so I put it back together and it ran good, until it blew the inner oring out after 5 mins!

when I pulled it apart the oring had sucked down into the groove around the bore, which then split it and caused it to fail.

So I really need to get on top of this because otherwise it usless to me. I didn't get out second gear but the bike was heaps more responsive.

PLEASE HELP ME!

what should I be looking for

I should have studied you first pictures ( I focused on your power loss) but this is what I don't like:
Hard to tell from the picture but it looks like there erosion/pitting around the inner o ring groove and some compression has been going around the inner o ring and the coolant may have been too if your o ring ended up in the bore. Are you sure you have the correct o rings?
Has your coolant ever been low?
The erosion/pitting near the o ring groove and possibly a warped head/cylinder could be why and would explain why the PO had everything gooped up with silicone.
If you don't have the tools to check your head and cylinder for flatness, most machine shops that I know of would do it as a courtesy.
It would be better to have better pictures or see the parts.
Good luck and let us know.

Ive uploaded photos of how the oring sucked deep into the inner oring groove, not into the bore. Ill take the head and cylinder in tomorrow to a machine shop and see what they say.

The orings I used this time around were the proper husky ones, I have rang the PO who put me onto the business who did the overbore and he is sending some orings that he says are higher temp and slightly larger in diameter to handle the 300 size bore? I doubt this will fix the issue though, I think theres an underlying problem somewhere.

I haven't really noticed the coolant level being low because ive hardly riden it, I rode it for 30 mins and then noticed some coolant out overflow when putting on trailer, at home I started it up and it was pumping out overflow from cold.

replaced orings and they blew again, and that's where im up to now.

is the inner oring groove meant to have a small section that continues down? like where the oring has sucked into? or is it suppoused to be a solid groove like the outer?

Not sure what you are referring to exactly, but the inner ring groove should be concentric like the outer one.
I think if you take your parts to a shop they will be able to tell you what is wrong.

See the 3rd and 4th photos in the lot I just put up? the oring has sucked into the groove.

Yes, I did see, but it's hard to know looking at your pictures. Take the parts to a shop