2003 RM250 hissing noise

Bfogg217
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Bfogg217
Took the bike out this weekend and spun a few laps. About 20 minutes in, I hear a hissing noise very similar to what I would expect air leaking out of the fork or shock to sound like. I pull off and check everything over real quickly and see nothing glaring. I ride some more and don't hear it again for another 5-10 laps. I can't find anything that sticks out to me as a "shade tree" mechanic that would point to an issue. I can cycle the suspension with my body weight in the garage and get no noises. I don't see any leaks anywhere and nothing appears to be broken. Tires are holding air just fine as well. I'm baffled and wanted to ask around to see if anyone else had experienced anything like this before or might have any ideas as to what is happening. I know it's sort of an impossible question to answer without actually touching the bike, but thought it might be worth a shot. Thanks in advance for any help
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KooyaKooya
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KooyaKooya 2/22/2017 1:07pm
2/22/2017 1:07pm
It might be your fuel vent line. Next time you hear the hissing noise, plug the vent line with your finger and see if it stops.
Bruneval
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Bruneval 2/22/2017 2:37pm
2/22/2017 2:37pm
Have you checked your radiators? If the head gasket has gone, it will pressurize the coolant system and you might be hearing it venting somewhere, not necessarily the overflow hose. One thing to check.
Bfogg217
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Bfogg217 2/22/2017 2:48pm
2/22/2017 2:48pm
Bruneval wrote:
Have you checked your radiators? If the head gasket has gone, it will pressurize the coolant system and you might be hearing it venting somewhere, not...
Have you checked your radiators? If the head gasket has gone, it will pressurize the coolant system and you might be hearing it venting somewhere, not necessarily the overflow hose. One thing to check.
I checked the radiators and I'm not loosing any coolant. The noise seems to be suspension related I'd assume as I'm hearing it as the suspension compresses I believe. It's almost like if you took the fork pressure release screws out and rode without them. It's such a strange noise and I can't replicate it off the track so it's hard to figure out. Thank you for the info though
xnationalwrench 2/22/2017 5:47pm
2/22/2017 5:47pm
You didn't say what bike you have so if your bike has schrader valves (in the fork) check the o-rings for cracks or splits which can let the air pressure to escape.

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Dtat720
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Dtat720 2/22/2017 6:14pm
2/22/2017 6:14pm
xnationalwrench wrote:
You didn't say what bike you have so if your bike has schrader valves (in the fork) check the o-rings for cracks or splits which can...
You didn't say what bike you have so if your bike has schrader valves (in the fork) check the o-rings for cracks or splits which can let the air pressure to escape.
Its in the title. 03 RM250..... I have the same bike. No schraders in stock form. If aftermarket bleeders are on it, it could be an air leak at the valves. being that the forks are open bath style, i would think if the forks had a leak you would have fork oil leaking as well
Bruneval
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Bruneval 2/22/2017 7:24pm
2/22/2017 7:24pm
Are they twin chamber 47mm Showa on the '03 RM250? I know that Suzuki used this fork on the RM models around that time, and if so, this is what they look like stripped down (from my RM125).



It could be one of the o-rings on the inner chamber. These chambers need to be completely full of oil and then pumped to remove the excess when you reassemble. If the seal has gone, it might have some air inside and potentially that is what you can hear.

Dtat720
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Dtat720 2/23/2017 4:59am
2/23/2017 4:59am
They are single chamber KYB if they are the stock forks
Bfogg217
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Bfogg217 2/23/2017 8:02am
2/23/2017 8:02am
Dtat720 wrote:
They are single chamber KYB if they are the stock forks
They are stock forks as far as I know. If the forks are leaking air, would they be leaking oil as well? Also, shouldn't I be able to replicate that issue by just compressing the forks with my body weight?
Dtat720
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Dtat720 2/23/2017 9:11am
2/23/2017 9:11am
Dtat720 wrote:
They are single chamber KYB if they are the stock forks
Bfogg217 wrote:
They are stock forks as far as I know. If the forks are leaking air, would they be leaking oil as well? Also, shouldn't I be...
They are stock forks as far as I know. If the forks are leaking air, would they be leaking oil as well? Also, shouldn't I be able to replicate that issue by just compressing the forks with my body weight?
Air pressure builds with heat so in theory you could warm the forks up with a heat gun and push them through the stroke and see if they leak. If thats possible to replicate, i have no idea but in theory it would. They are open bath forks, the oil is in the main chamber under the caps. So if you are leaking air in the down stroke, oil is there as well and should be forced out under the pressure. When is the last time they were freshened up? The oil may be super thick and worthless.

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