Crankcase Breather--I should have done this a year ago

Saturday I went to the hardware store and picked up three feet of 1/2" ID braded PVC #048643-025707. This is a flexible clear PVC hose with an internal (inside the PVC) loose nylon weave reinforcement. It has a 1/2" ID and a 3/4" OD. I also purchased a UNI filter breather filter UNI part # UP 123. This breather filter has a 1/2" input flange to fit inside the flexible PVC tubing.

I removed the stock crankcase breather hose and using a hose clamp attached the flexibel PVC to the top of the cam cover where the stock hose attached, then ran the tube up the left side of the frame and terminated it behind the headlight / number plate. I had to sligtly rotate one of the hose clamps holing the left radiator crossover tube but no big deal. I then checked out the lock to lock steering action and cut the hose to length so it stayed behing the Number plate area as the front end is turned. I then attached the UNI filter using a hose clamp and its done. I ended up using 20" of flexible PVE hose.

No more dripping, no worries about sucking water in the hose if starting the bike in a stream unless it is over the bars!!

Fired the bike up went out for a 55 mile loop everthing worked great. Could not be happer just should have done it a year ago, guess I was being lazy every owner should do something like this for the stock breather hose.

Remember my bike is dual sported so I do not have the stock voltage regulator on the frame this may be a problem for routing clearence but I do not think so.


[This message has been edited by Clark Mason (edited 07-09-2000).]

Thanks for this re-route instruction Clark. I will be jumping on this band wagon early!!


Excellent .... Ill get on it this week!

Thanks Clark


Nathan Apelbaum

99 WR400F IMS Seat/Tank,Scotts full suspension mods,Fastlines front line w/CR routing,Scotts Tripletree,Dampner and Protaper combo,Big Gun tapered header and muffler,W.R.D. 7.5oz flywheel weight, de-octopussed, Ricky Stator rewind, Air box lid off,UNI Air filter,DSC legalizer kit,Dunlop K139 Frt D606 rear and a couple of other little bits

I took my 98 WR on my first quick ride today (I’m still stupidly grinning). The only thing I noted on the post ride inspection was the trace of oil coming from the breather tube. No big deal, but it made me think of the Uni filter I ran on the breather line of my XR which was routed up near the airbox. This was a pretty good preventive measure in extreme dusty or wet conditions. Once again Clark has done all the homework and testing of another hot setup I will soon be implementing. Thanks Clark!


I tried this mod back in '98. I mounted the filter behind the shroud/radiator. It worked great for a couple of rides. Then the filter got saturated, and I had an oily mess all over my shrouds, tank, etc. I went back to the stock hose. As an MXer, I don't forge creeks, nor do I start my bike midstream, so I have no concerns about sucking muck up the tube.

Scott F


Thanks for the tip on posible oil getting up to the breather filter. I will keep an eye out for it. I did do power runs through max rpm and tried to get the oil up to the filter. However, on post ride inspection I saw none. I will keep you observations in mind and if a problem come up with another solution.



My XR filter would get saturated (and sometimes messy) on some of the longer rides. Cleaning it was very simple and just became another perioidc maintenance item. I would expect the WR will be no different.


if you dropped your bike cylinder downhill, how much oil could you loose out the filter?

If you drop your bike upside down on a hill with the top of the bike pointed down hill I recommend you get it right side up a soon as practical as the oil will start out the vent tube and through the filter. This is a drawback kinda like my old 97 Husabserg 600. Dropped the Husaberg upside down hurt myself a little when I tried to start the bike the top End filled with crankcase oil and hydro locked!!! The Husaberg crankcase breather flows right into the frame backbone which is the input to the carburetor and a straight shot into the head. Plus running with Oil getting in through the carb all the time made plug reading a real art. My solution same as here I routed the breather behind the number plate and it worked great for two years before I sold it and it is stilll working fantastic. Man that built 600 was fast I mean a easy 108MPH with stock gearing and it pulled it easily.


My upside-down PCV valve is still working great, no muss, no fuss. Three weeks ago I totally submerged my WR in a deep water crossing in the Sequoia's. When I drained the oil at home, no water at all. It was still fresh, clear and light honey colored :)

whats a pcv thing and where does it goe cheer new boy to the wr thing

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