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Discussion Starter · #1 ·
So I just noticed a strange hissing sound, like compressed air being let out, coming from somewhere near the key iginition area after rides. I can't replicate it and it doesn't happen all the time. I noticed it for the first time yesterday after a 30 mile ride and then again after a 10 mile ride. After I turned off the bike and heard the hissing sound. Is there anything up there in relations to the front suspension that might be releasing air? My front brakes don't work so well, could it be released compression from them?



I've pumped the front shocks up and down for a few minutes to see if any hissing comes but nothing so far. I've also pumped the front brakes quite a bit. I just can't seem to intentially replicate the sound.



Kinda unrelated but I think I have a squeaky Pro-Link and it is driving me nuts. Everytime I bounce on the bike the back end squeaks. I've lubed everything I could think of but I've heard the Pro-Links have internal squeak problems which I doubt I'm equipped to fix. :-(



Any suggestions? Thanks!
 

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So I just noticed a strange hissing sound, like compressed air being let out, coming from somewhere near the key iginition area after rides. I can't replicate it and it doesn't happen all the time. I noticed it for the first time yesterday after a 30 mile ride and then again after a 10 mile ride. After I turned off the bike and heard the hissing sound. Is there anything up there in relations to the front suspension that might be releasing air? My front brakes don't work so well, could it be released compression from them?



I've pumped the front shocks up and down for a few minutes to see if any hissing comes but nothing so far. I've also pumped the front brakes quite a bit. I just can't seem to intentially replicate the sound.



Kinda unrelated but I think I have a squeaky Pro-Link and it is driving me nuts. Everytime I bounce on the bike the back end squeaks. I've lubed everything I could think of but I've heard the Pro-Links have internal squeak problems which I doubt I'm equipped to fix. :-(



Any suggestions? Thanks!
mm,odd one,id hazard a guess that the air in your fork expands,with heat/use.then leaks out after a ride.

what pressure are you running in the forks?
 

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My first thought was the air lines to the forks, so check to see what pressure you have there. The valve cap should be on the right fork if it's stock. There is a crossover line between the two, and you might put some soapy water on the lines, then pump up the forks to the recommended 10 to 16 PSI, and see if you spot any bubbles.



The second thought was possibly a pressure leak from the radiator cap, or even the thermostat area. When was the last time you serviced your cooling system?
 

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The second thought was possibly a pressure leak from the radiator cap, or even the thermostat area. When was the last time you serviced your cooling system?
good shout Ramp
 

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In this pic, the inset on the left with 33, 16, 17 is the valve, and you can see the crossover hose 24 to the left fork. Spray soapy water on all the areas after you pump up the forks to 16 PSI, and see what you get. By the way, make sure you use a HAND PUMP not a shop air compressor.

 

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Discussion Starter · #6 ·
Thanks a ton everyone for the sound advice. I will try the soapy water trick tonight once I get home. Really hoping it is a simple fix! I haven't noticed any drop in performance or anything like that so hopefully iy won't turn out major.
 

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Discussion Starter · #7 ·
EDIT: Forgot to add info about the cooling system. This is a recently purchased bike and I have no idea of history of the bike. I haven't flushed anything yet so I suppose I should start with that. Other than this mysterious hissing and the squeaky Pro-Link I've had no problems with the bike. *knocks on wood*
 

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MechaJubei, with you being in Spokane, I know a gal from the Shadow board there that is really a good bike wrencher, so take a look HERE, and look for KathyM. She might have some basic helpful ideas too.



Joel in the Couve.
 

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Discussion Starter · #9 ·
Thank you Joel for the lead, I will definately try and look her up.



Just an update on this issue. I think I narrowed it down to...the gas cap? I could find no leaks in the front brake cabling nor the radiator cap as suggested. I just happened to have my head near the gas tank when the hissing appeared again and it really did sound like it was coming from the cap.



This only happens on very hot days. Is it possible the gas evaporating is escaping through the gas cap? Is this normal? None of my other bikes ever did that...I be confus-ed.
 

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If it's your gas cap try popping it off when you hear the hiss. If it's the culprit you'll be rewarded with a sudden pressure equalisation which should make a noise. If that's the case, you should check the vent in the cap for obstruction and give the gasket a light wipe with oil or grease to help it seal.



Anything else and I say do the soap thing and look for the bubbles.



Or it could be snakes...





But if you start to hear a weird chattering sound...

 

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............... My front brakes don't work so well, could it be released compression from them?................


A note on your brakes. They probably need a good cleaning. I just went through this on my 81 CX. Let me know if you'd like any info/help.
 

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If this is your gas cap hissing which means it's vent hole/holes are almost totally clogged to the point that the air pressure is just barely escaping once it builds up (causing the hissing noise) I'm stunned it was still working good enough to allow the fuel to keep flowing enough to keep the bike running right.



The fact that it might be the gas cap does make sense though and not the air forks because once the pressure has leaked out of the air forks it wouldn't KEEP leaking and making a hissing noise after every ride unless you were re-filling those fork tubes back up with air over and over.
 
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