Crank case breather tube length?


15 replies to this topic
  • bcone

Posted February 04, 2007 - 11:12 AM

#1

Is there ANY reason that I should not cut this to be as short as possible:excuseme: ?
It runs from the case to the air cleaner and goes around the block a few times to get there
I can't see what the legth of tube has to do with the function, is this left over from when it was desmogged?

  • frankstr

Posted February 04, 2007 - 07:13 PM

#2

are you working on..

  • bcone

Posted February 04, 2007 - 07:42 PM

#3

Sorry :ride: 96' XR650L desmogged. Does that really matter?:ride:
Breather just goes from the airbox to crank case. Can I cut it or not?

  • cleonard

Posted February 04, 2007 - 10:24 PM

#4

Sorry :ride: 96' XR650L desmogged. Does that really matter?:ride:
Breather just goes from the airbox to crank case. Can I cut it or not?


You can, but it might not be the best idea. When the piston goes up 650cc of air get sucked in. When the piston goes down the air comes out. You don't want it to suck in dirt. The main reason it goes to the air box is smog related. The idea being that any hydrocarbon containing gases get sucked into the engine and burned. On the XR600 it just sort of ends near the top of the airbox. There are little filters available for the breather.

  • bcone

Posted February 04, 2007 - 10:35 PM

#5

I just want to shorten it. Possible or some hidden down side :ride: ?

  • Kawabuggy

Posted February 15, 2007 - 08:04 AM

#6

As long as it terminates where it is supposed to (on both ends) the length of the hose or routing should not matter at all.

  • OUTERLIMITS

Posted February 15, 2007 - 08:36 AM

#7

I just want to shorten it. Possible or some hidden down side :censored: ?


I'm more familiar with the 650R, but it's the same basic idea. You want that tube to be long enough (high enough) to clear any water issues. Your best bet is to take it directly up under the seat or to the frame backbone and cap it with a Uni crankcase filter. Nothing good performancewise can come from having crankcase fumes pumped back through the carb. They put it there for EPA reasons. You can make the tube short if you're not worried about water entry, but by all means put a filter on it. I will say however, that I had a KLX650R with the same vent except it came off the top of the valve cover and went down from there . What happened there was that at high revs oil would blow through the line. I ended up rerouting it up near the handle bars with a Uni filter and it ended the problem.

  • roadrunner81

Posted February 15, 2007 - 09:15 AM

#8

Has anyone tried or thought about running a one way valve on the end of the breather. A friend of mine has a crf450 and it looks as though it basically uses a pcv valve to allow the motor to push air out but not allow it to re-enter the crankcase causing an absence of pressure.

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  • OUTERLIMITS

Posted February 15, 2007 - 09:49 AM

#9

Has anyone tried or thought about running a one way valve on the end of the breather. A friend of mine has a crf450 and it looks as though it basically uses a pcv valve to allow the motor to push air out but not allow it to re-enter the crankcase causing an absence of pressure.


Did that on my KLX for a very brief time until I started thinking it all through. I'm almost sure that you want to let the engine take air back in. Not sure what could happen, but certainly didn't want to find out.

  • cleonard

Posted February 15, 2007 - 11:26 AM

#10

Has anyone tried or thought about running a one way valve on the end of the breather. A friend of mine has a crf450 and it looks as though it basically uses a pcv valve to allow the motor to push air out but not allow it to re-enter the crankcase causing an absence of pressure.


You will end up with a pressure differential between the crankcase and the outside. This may result in blowing seals. The 650R is already known for blowing the countershaft seal and this could make it even more likely. You will also loose a little power as now the piston will be creating a vacuum inside the crankcase when the piston goes up. PCV valves work on car engines because when one piston is going up another is comming down. The only gas that goes out the PCV valve is what leaks across the rings.

  • platterdr

Posted February 15, 2007 - 04:40 PM

#11

the hose length should not matter it's not like that hose is special made for a desmog job anyway the bends and curves if anything would slow the air down(maybe). I didn't cut mine but I can't see where that would make a difference. But if your engine seizes up please let us no so next time we can tell someone the correct info:ride: on

  • roadrunner81

Posted February 15, 2007 - 05:28 PM

#12

Cleonard, I thought about it for a while and although I think you wrong about the seals I do think your correct in assuming the engine would be a little sluggish due to the vacuum under the piston.

  • jersey jorge

Posted March 20, 2007 - 06:18 PM

#13

i don't know...looked at it and cut it about in half and reattached... just started playing on the bike... this is new to me but its a 97... looks like this when done...

Posted Image

i guess it could suck in some crap from the airbox but i was really concerned about the vacuum caps... it said in the IMS directions to pull two or four vacuum lines and cap... so i did...looked like some of that stuff should be needed but i guess not... anyone want to confirm this for me?

here is one on the right side...

Posted Image

and this one on the bottom of the carb...

Posted Image

and looking at it you can see the bend in the hose and the capped vacuum...just keeping up with the thread... :applause:

and the last two caps...on the right side...

Posted Image

now keep in mind i got this bike down to some bare bones... so it will look different from your ride ...


ok here is a pic...

Posted Image

i think we are good with the shorter hose... :eek:

  • CTXr650L

Posted March 21, 2007 - 02:38 PM

#14

i shortened up that hose on mine when i desmoged it to, doesnt seem to be a problem as long as there are no kinks in the line. that cap on the bottom of the carb can come off, thats just a fuel drain when you unscrew that screw above it.

  • XR650L_Dave

Posted March 22, 2007 - 07:56 AM

#15

i don't know...looked at it and cut it about in half and reattached... just started playing on the bike... this is new to me but its a 97... looks like this when done...


i guess it could suck in some crap from the airbox but i was really concerned about the vacuum caps... it said in the IMS directions to pull two or four vacuum lines and cap... so i did...looked like some of that stuff should be needed but i guess not... anyone want to confirm this for me?

here is one on the right side...



Posted Image


This is the valve that richens the mixture on decel. If you have popping, you can connect this back to the nipple on the front of the carb above the intake.

Dave

  • XR650L_Dave

Posted March 22, 2007 - 08:00 AM

#16

Has anyone tried or thought about running a one way valve on the end of the breather. A friend of mine has a crf450 and it looks as though it basically uses a pcv valve to allow the motor to push air out but not allow it to re-enter the crankcase causing an absence of pressure.



This will cause the crankcase to almost always be at negative pressure.

It would probably lessen the chance of blown seals, but since air would always be trying to get into the engine past the seals you might suck in some crud (not likely) or you might cause some premature seal wear.

Drag racers use a trick similar to this to gain a few HP.

Dave





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