KTM Breather Hose Mod....How much air is meant to come out?

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pdee4t

Hi everyone.
I installed a one way check valve for the crankcase vent hose, as I had originally gotten water up through the vent hose. Did a bit of research online and worked out that quite a few KTM owners have installed one way check valves on their KTM's.
I bought a specially made check valve for it then vented the breather hose to the atmosphere, around the tank, then just underneath it to the other side of the bike....but when I put my finger just in front of the open end of the hose, I can barely feel any air escaping(it's very very faint).
When I put my finger over the hole and block up the hole for a second or 2, I can feel a bit more coming out and some very light vibration, but not very much, especially compared to my mates Yamaha YZ450.
it does increase with more rev's...but still not very much.

Im wondering if any other KTM RFS owners can verify how much air is meant to come out of the hose or if theirs is the same?
and also why the Yamaha's have a lot more air coming out, is it because the hose on the Yamaha's comes from the very top of the engine?
Apart from that, it runs and idles fine with it vented the way it is now. Not burning any oil or anything.

It's a 2004 EXC for those wondering.
 
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Mihylo33

Mihylo33

Probably just a little extra blow by from the piston an probably slightly increased back pressure created by the check valve. You're fine.
 
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pdee4t

im just wondering, in case the check valve ever fails, if I could use something like this instead on the crankcase breather hose?
the old Yamaha's and XR400's have em. Would that work for what I want to do?(stop water getting in but allowing the air to still vent out)?

3302739.jpg
 
Mihylo33

Mihylo33

pdee4t:
im just wondering, in case the check valve ever fails, if I could use something like this instead on the crankcase breather hose?
the old Yamaha's and XR400's have em. Would that work for what I want to do?(stop water getting in but allowing the air to still vent out)?

3302739.jpg
Click to expand...


Yep. It's all I use.
 
P

pdee4t

Mihylo33:
Yep. It's all I use.
Click to expand...

How would the air coming out of the breather hose escape though if the end of the hose hose is plugged up with 1 of those drain tubes?
From what I can tell, the tube is sealed at the end of it?
 
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Mihylo33

Mihylo33

pdee4t:
How would the air coming out of the breather hose escape though if the end of the hose hose is plugged up with 1 of those drain tubes?
From what I can tell, the tube is sealed at the end of it?
Click to expand...


It's just a closed end with a slit in it. Positive crankcase pressure keeps moisture from going in and keeps air going out.
 
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pdee4t

Mihylo33:
It's just a closed end with a slit in it. Positive crankcase pressure keeps moisture from going in and keeps air going out.
Click to expand...

My bike only has a very tiny amount of air come out of it though, like barely any. Will that be enough to come out the slit in that drain tube?
 
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