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motoman196

front fork issue hissing noise

6 posts in this topic

I posted this in the 250f forum but thought maybe you guys would have some input as well being that the forks are the same. I posted this in the suspension forum and got no feedback any help is much appreciated. I own a 2004 yz250f. I went to the track two weeks ago and I started hearing a hissing noise like air escaping from the front forks of my bike when landing off of the bigger jumps. I noticed a little bit of dust build up at the bottom of the fork so I thought maybe the fork seals are leaking a little. Turns out one fork tube was seeping, but not enough to get by the dust seal. Anyway I put new fork seals in . No leaks, but still getting the same noise. I then started thinking maybe its the fuel cap breather hose, but onlookers told me they could hear the noise too!!! No way that breather hose is releasing that much pressure plus I have never heard the noise before until recently. It's got to be the forks. It makes me cringe :thumbsup: when i hear the noise. Any ideas on what this could be. Please help!

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so it was hissing b4 you replaced the seals and oil right?

did you check the pressure release screw..maybe it isnt seated correctly..

my only guess is

1)Oil insufficient or too thin

2)Spring weak or broken

3)Front fork air pressure high

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I have opened the release valves they are holding air in becauase when I open them I can hear air coming out. I just put new springs in about three months ago. They are yz450f springs. I didn't use fork oil instead I used mobile 1 fully synthetic ATF. That shouldn't matter though because the noise was present right before I changed the seals. I'm running the fork oil height at 115mm from the top of the tube. I'm stumped???:thumbsup:

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If the pressure release screw is used there is not much way pressure can make this noise. I am reaching here but could the noise be coming from the breather hose from the top of the cylinder?

To check if it is the tank when it is hissing - put your finger over the end of the gas tank breather hose

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I can not get it to make the noise when not riding. It will only hiss when landing off the bigger jumps at the tracks. So I'm thinking it's only doing it when the suspension is bottoming or close to bottoming. It makes a shhhh noise don't know if hiss was the right way to explain it.

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