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Old Streetfighter Motorcycle Forum Post 08-26-2018, 01:11 AM   #409
shinyribs
Is my bike ok?
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Default Re: Shiny's adventure with dirtbikes

Step away from the XL for a bit and show some love to the XR4. I mentioned earlier that I can fly on the little XR250 compared to the 400, but there's not a huge difference in weight. I actually weighed them myself and there's only about a 20lb difference. Admittedly, the 400 holds it weight a little higher, but damn...that torque. Even though the fork on the 250 is extremely basic ( basically a damper rod with a non-adjustable compression cartridge snuck inside) it is veeeeery plush in the woods. It doesn't take a whole lot to overwhelm it, but up untilit starts bottoming it, it's great. So I decided to dive back in the the 400 forks and really make a difference.

This is what I found. The compression valve is stoopid. It's a bending shim valve, but it's reverse bending- meaning the I.D. of the shims bend in to flow oil vs the outer lips lifting.

Oil flows through these parts left to right. Only one shim shown, but stock carries 12 shims. A popular "mod" is to remove 6 of the 12 shims and lots of guys rave about it. I did it and saw nothing. These forks are known to be harsh. Playing with the external clicker on the base valve shows zero effectiveness on the bike. Playing with the clicker with the valve in my hand I saw that the clicker valve can completely stop all oil flow. That tells me that a lack of oil flow is what's choking up the system, not just being out of adjustment. If there was adequate oil flowing through the valve and shims then the clicker would be effective.



Here's how much of the top plate the shim blocks. Keep in mind the inner portion of the shim needs to bend in, and the oil pressure being directed way towards the outer edges where it is supported by the bottom plate of the valve. This makes no sense to me. Scribed a line to show exactly where the shims sits.



I chucked the top plate up and removed some material to allow more oil flow towards the I.D. of the shim, then I drilled the oil holes slightly larger while angling the holes towards the I.D., too.

Stock vs modified




Reassembled everything (with only 4 shims)and took the bike for midnight run through a short section of trail. Is it perfect? Probably not. Was there a difference? Hell yeah! I was pretty happy with my recent tuning on the rear shock, but now all I feel is harshness out back. That tells me the forks are now soft enough that I'm noticing the shock needs more work.

I'll log some more miles tomorrow to really make a decision, but it feels like I'm on the right path.
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