USD 43mm Fork valving

Kawasaki KDX 250
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Liberated
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USD 43mm Fork valving

Post by Liberated » 01:23 pm Jan 31 2015

I'm sure I'm beating a dead horse here but I thought I would share my experience with the stock KYB 43mm fork. I just picked up a fairly low hour 92 250 and really love the motor.... hate the suspension. I took it out once to Holister Hills and was glad for all the power... it was more comfortable to Wheelie over everything then have the fork try to control the bumps... After much searching I know my only way to go would be to swap out for a later model front end... well, the fleebay is pretty picked over and this was supposed to be a budget friendly 2 stroke for me to play with.

I ended up disassembling the fork and contemplating how the fluid moves through the basevalve. It was much different then I was prepared for. I ended up Modifying the piston and check plate myself for better flow and purchased a set of springs for my weight...

Now I know there are few of these around and even fewer with the stock forks.. but I'm here to tell you, they can be modded and you can get really good performance from them!! I actually enjoy riding it now... it performs nearly as well as my 2008 Husqvarna with properly valved forks.

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Re: USD 43mm Fork valving

Post by KDXGarage » 02:35 pm Jan 31 2015

Welcome to the forums. Can you describe more about what you did to the forks?
Thank you Julien D for all your hard work!

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USD 43mm Fork valving

Post by Liberated » 08:25 pm Jan 31 2015

Sure thing. A condensed version.. I measured the port area on the piston and check plate. The fluid has to pass through the check plate first before it can flow through the piston. I found the plate's ports had 40% of the area of the piston's ports... So I enlarged and shaped the ports on both the check plate and the base valve piston. I was sure the changes would allow more oil flow, however I was not sure the flow would have a meaningful effect. An item of note is that the clicker port is a very small percentage of the overall available port flow... so adjustments at the bottom of the fork leg really offer only fine tuning...

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Re: USD 43mm Fork valving

Post by KDXGarage » 04:43 am Feb 01 2015

Are you talking about the stock part, as I have shown on the left of my picture?

Thanks.

Image
Thank you Julien D for all your hard work!

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USD 43mm Fork valving

Post by Liberated » 01:42 pm Feb 01 2015

Yes, I am speaking of the stock valve. I had heard there were gold valves available at one time, however I understood they are no longer available. I also posted in my original post that this was to be a budget bike for me to play with. A free mod to the stock piston that works is awesome in my book.

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Re: USD 43mm Fork valving

Post by KDXGarage » 04:44 pm Feb 01 2015

Hopefully the Race Tech Gold Valves are still for sale for the KDX's.

That is indeed an awesome job. I have heard of someone doing that to a more modern KX piston, but did not think of that on the KDX250 piston. Great job to make it better for you!

Where did you find springs? I have recently seen a couple of guys paying $170 or so for older model KX springs that are custom made. That sounds pretty expensive.
Thank you Julien D for all your hard work!

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USD 43mm Fork valving

Post by Liberated » 08:49 pm Feb 01 2015

I ended up contacting Cannon Racecraft in OK... they will wind you anything you want, but their stock springs are a bit cheaper if they fit your bill. They had a set just right for me on their dimensional list, so I grabbed them. I would post some photos of the piston mods..... if I could only figure out how to upload them.... Perhaps I need glasses.

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Re: USD 43mm Fork valving

Post by KDXGarage » 11:51 pm Feb 01 2015

Ah, yes they make custom springs.

Usually photobucket and other sites can host pictures.
Thank you Julien D for all your hard work!

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Re: USD 43mm Fork valving

Post by snopro753 » 11:07 am Oct 16 2015

Long shot, but I sent Liberated a PM and would like to get his pictures so I can post them here for others and myself to see.

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Re: USD 43mm Fork valving

Post by Liberated » 12:29 pm Oct 16 2015

Apparently I'm not authorized to view pm's,.... I guess they will die with me :grin:

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Re: USD 43mm Fork valving

Post by snopro753 » 12:12 pm Oct 19 2015

Here are the pictures Liberated sent me of his mod of the KDX250 Fork Piston

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Re: USD 43mm Fork valving

Post by snopro753 » 09:45 am Oct 21 2015

Liberated, thank you for sending me the pictures. I have posted them above. How did you chamfer and enlarge the holes? Dremel? Looks like a steady hand is needed.

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Re: USD 43mm Fork valving

Post by Chuck78 » 06:42 am Aug 13 2018

Any chance of getting these photos and any additional tips on this re-posted? Were the valving spring shim washers in the base valve reconfigured as well?
'99 KDX220, 74 Rickman VR250, '77 Suzuki PE250,
'77 Rickman CR900/GS1105cc, '77 Suzuki GS750-920cc, '79 Suzuki GS425-489cc racer build, '77 Suzuki GS550-740cc canyon carver, '62 GMC 1000 Panel Truck

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Re: USD 43mm Fork valving

Post by MikNY » 06:41 pm Dec 29 2018

Trying to rehab some usd 43 from my 94, anyway to get these pics back?

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Re: USD 43mm Fork valving

Post by KDXGarage » 09:05 pm Dec 29 2018

Yeah. I would like to see them, too. I need to try to email him.

What are you looking to do on your forks? I have a pic of some I took all the way apart years ago... Somewhere on my laptop
Thank you Julien D for all your hard work!

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Re: USD 43mm Fork valving

Post by KDXGarage » 12:39 am Dec 30 2018

I sent snopro a PM. We shall see.
Thank you Julien D for all your hard work!

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Re: USD 43mm Fork valving

Post by snopro753 » 02:04 am Dec 30 2018

I got your PM. I need to look through my old hard drive for these pictures. If I find them I will post them again.

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Re: USD 43mm Fork valving

Post by KDXGarage » 03:19 am Dec 30 2018

Great! Thanks!
Thank you Julien D for all your hard work!

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Re: USD 43mm Fork valving

Post by snopro753 » 11:22 am Jan 13 2019

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Re: USD 43mm Fork valving

Post by KDXGarage » 12:29 pm Jan 13 2019

THANK YOU, snopro753!!

:partyman: :supz: :boogie: :prayer:
Thank you Julien D for all your hard work!

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