Breather Tube?????

20 replies to this topic
  • novaman64

Posted June 10, 2004 - 06:46 PM


So I have a CA model 250X and pulled the air pump off and installed the Baja Designs blobk off plates. When I was putting the cap onto the airbox I noticed that there was another tube that goes to the airbox. The toob is some kind of breather that runs from the head, then splits and one goes down to the swingarm where there is a plug in it, and the other goes into the airbox. See the pics because I am proly confusing everyone right now.

Now to the question.... When I pulled the black plug out of the swing arm end and bunch of condensation came out, wouldnt it be better jsut to leave this plug out all the time? Next part is can I completely eliminate the line that goes into the airbox? The reason behind this is that all it is doing is injecting hot air into the motor. However I dont know if it creates needed vacuum. Thanks for the help.
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  • Throttlejockey

Posted June 11, 2004 - 12:36 AM


That plug is a vent and if you leave the plug out it will suck dirt and water up it into your motor. Do not leave the plug out.

  • motomadman

Posted June 11, 2004 - 05:44 AM


Yeah, what's the deal with that water collecting tube?

Sure, it's condensation, but why don't Yamaha's have these tubes. Do any other bikes wave these tubes?

It just seems kinda strange. I didn't see 'draining the tube' as a maintenance item in the manual :thumbsup:

  • YZDAD1

Posted June 11, 2004 - 06:19 AM


If you set it up "Yamaha Style" it's worth 1/2 to 3/4 horsepower! :thumbsup:

  • Moto_Squid

Posted June 11, 2004 - 06:31 AM


and what is yamaha style?

  • YZDAD1

Posted June 11, 2004 - 03:51 PM


Run the breather hose from the valve cover to "atmosphere" and cap the fitting on the airbox. This let's the engine breath fresh air and not suck the oil & blowby back into the carb/combustion chamber.

  • RaceyYZ250F

Posted June 11, 2004 - 05:01 PM


yea thats water that gets into your airbox, instead of sitting right under the airfilter and possible chance of getting sucked up it puts it down that tube to hold until u empty it, the cap must be put back on other wise mud could getinto there and clog it and into your motor! and the pic that shows a tube going to the head, thats a different tube, this one with the cap goes straight to the airbox.

  • Throttlejockey

Posted June 11, 2004 - 05:05 PM


the pic that shows a tube going to the head, thats a different tube, this one with the cap goes straight to the airbox.

Which also has a T on it that connects to the valve cover breather.

  • Getto

Posted June 11, 2004 - 06:40 PM


You will get water and oil in that tube... Sythetic oils are hydroscopic, they collect water from the atmosphere. :lol: That tube is at the highest place in the motor so that when the water evaporates from the oil, it finds its way to the tube, where is cools and stays !! :lol: The oil comes from it slashing around in the rocker cover, I guess :thumbsup:!! I agree, DO NOT leave the plug out of the end, but by all means, disconnect it from the airbox, thats just emission control crap !! :awww:

  • HighRev

Posted June 11, 2004 - 08:41 PM


FYI it's hygroscopic not hydroscopic. G'day mate. Scotty

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  • novaman64

Posted June 11, 2004 - 09:33 PM


By disconnecting it from the airbox wouldnt it make the system completely sealed since the end is capped? And if it was sealed would the water still have a tendancy to go into it?

  • HighRev

Posted June 11, 2004 - 10:31 PM


? #1 Yes,? #2 No.I don't think this is a good place to look for performance gains.The system evacuates piston and exhaust valve blow-by from the crankcase.DO NOT PLUG IT UP.Open to atmosphere might be okay but if it has an EGR valve..... :thumbsup: Scotty

  • YZDAD1

Posted June 12, 2004 - 01:24 AM


If you disconnect the "T" fitting from the Honda setup you must:

1. Cap the fitting on the airbox so as not to suck in unfiltered air into the engine as this fitting is on the carb side of the airbox.

2. DO NOT! cap the end of the breather hose coming off the valve cover if you seperate it from the airbox. If you do the engine cannot "breathe" off the blowby produced by the engine running.

3. The engine CANNOT get water and or mud debris into it from this breather setup. When the engine is running it is producing crankcase PRESSURE that is being evacuated through the breather hose. Also, that is going to be quite a distance for debris/mud/water to travel along with it being uphill. I suppose if you're an Extreme jumping type and launch off into a 10' deep pond or mud pit with the engine shutoff then.................. :thumbsup:

  • crazymandan

Posted June 12, 2004 - 06:13 AM


By all means be careful routing that breather tube. I did some adjustments to the carb and stuck it back on, and apparently I rerouted the hose wrong. I went for my first hard ride and halfway through oil began to just spew out... The breather hose had been pinched off, and oil was coming out of the oil overflow... Not good... not good at all. But I fixed the problem once I rerouted it and opened up the tubes. So, be careful and make sure that the breather tube is always open for air!!!!! :thumbsup:

  • wiegand913

Posted June 12, 2004 - 06:46 AM


K&N makes a small breather filter for cars that may be a good idea to stick in the end of the breather tube after you take it out of the airbox. Posted Image

  • kelstr

Posted June 12, 2004 - 12:33 PM


if you realy want to run it yamaha style----look at the factory yamahas and or hondas they use the exhaust to siphon off crankcase pressure-----the stock yamaha vent tube is a 1950 chevy design and you dont want to run your slipper piston honda that way----the yamaha can get away with it because it has a larger crankcase and a heavy 2 ring piston and will be ok(kinda sorta) but can be made to make more power if it was siphoned out and the venting changed in the case------the california x that has the smog pump can be turned into a realy kool exhaust siphon, youve got all the plumbing and the port right there----the honda needs to have the draft from the intake to correctly pull presure out of the crankcase and not have to push it out like a the old design heavy piston yamaha ----you realy want to siphon it of with the exhaust but the intake does work, ive tested the 450 and the 250 several different ways of scavenging the crankcase pressure out and the exhaust works the best and the intake works very good also and just letting it try to push the presure out like the yamaha style vent when hot will lose power and soon contaminate the ring with oil and start burning oil now you get to rebuild your motor and start over---not good ------the moisture in the tube is just condensation and all motors make it --it dosent matter what kind of oil you have in the motor--it just depends on the % of humidity in the air and the due point -----this stuff is just all normal and ben around for ever------the tube should be drained offten and the oil kept kleen and do not over fill the crankcase ever.

  • cal44

Posted June 13, 2004 - 03:32 AM


Rewriting my reply.I guess thinking at 4:45 A.M. is not good sometimes!Engine displaces the air volume in crankcase.It needs to inhale and exhale.On the crf250x,Books are not clear on routing of intake side.The vacuum side,the one in question.We would want to extract any gasses.Keeping the oil cleaner.That T section that branches off in the picture?Where the plug is at.Could be a visual check for blowby(oil). :thumbsup:

  • YZDAD1

Posted June 13, 2004 - 06:32 AM


Anybody really ever thought that the OEM setup may be "helping" the CRF250's to run themselves out of oil? Plot it out, it's a closed loop system, the only "breathing is to breathe the crankcase back into the carb, then this blends with your air fuel mixture and burns. It does not find it's way back into the engine crankcase, and the carb pulls on the crankase, but that said, what causes the power to rise on the dyno when you vent the engine Yamaha style? It's one of the most noticable gains. :thumbsup:

  • wiegand913

Posted June 14, 2004 - 06:15 AM


i pulled the breater hose off the airbox and plugged the hole on the airbox. it made almost as much difference in power as the Bill's pipe! i guess burning hot oily air firing into the intake tract is no good for power after all!
i plan on putting on a filter like the one on my previous post. they sell them a summit racing for $16. really makes a difference in midrange power! :thumbsup:

  • CRFX_Rider

Posted June 14, 2004 - 05:00 PM


Here is the setup i just did.
Posted Image
It runs thru a small filter that is plugged into the airbox on the filter side.The small filter is not really needed but it also doubled as a airbox fitting.
Now it can vent into the airbox instead of being pulled directly thru the engine via the intake boot.

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