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yamahauler44

Engine breather hose question.

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i have a 1999 yz400f i have heard that re-routing the engine breather hose to the air box is good for creek crossings ect. what have you heard of this and would you recomend it?

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I put a tee in mine with one leg going down the original route (with a filter on the end), and one leg going to the air box. That way, if the down leg does happen to get submerged, the vent will suck from the air box, but if it blows a little oil, that will continue down the original down leg and not fill up my air box.

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I had done the same thing as Birdie, but with that huge tubing it looked ugly. For now mine is routed stock. The big thing is to route the carb vents to the airbox, because if they get submerged the motor chokes out. As long as they are vented to the airbox, the motor should stay running (under most conditions) when the bottom cases are under water and not suck any water up the vent hose.

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I rerouted the top carb vents to the air box and I rerouted the breather hose so the end opening is over the chain near the swingarm. The breather has a little more room before it's under water and the oil drops on the chain instead of the left peg. :)

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Make sure you get it up high somehow, if you stall out in a mudhole, it will suck mung up the hose and pour it all over your top-end. I found this out the hard way, and trust me, you don't want to do the same. At the very least, put some sort of filter on it, so that it only sucks up water and leaves the silt behind. I have since moved mine to run backwards along the frame and along the top of the airbox. If you search on this topic, there have been many posts about it in the past.

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since we are on this subject

I just recently got my 426 titled and have been riding it on the road...after riding for liek 30 minutes i notice oil dripping out of the hose-then i usually have to put 200ml of oil back in. I am running at kinda high rpm's and i'm search doing 4th gera wheelies isn't great but it seems after every ride liek this i have t fill it back up with some oil-is this normal-the bike runs great and doesn't smoke at all-this is the only place oil comes ffrom-probably time i gear it taller if i keep riding on the street?

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I always woried that mine would suck sand up into the top end when I am in the dunes but maybe not??? Or at least I hope not. :)

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The pressure in the crankcase changes from pressure to vacuum to pressure cyclically depending on which way the piston is going at the time. Only at low engine speeds does it have enough time to run nearly the full 450cc volume of air displaced all the way out or in through the vent. At cranking speeds, or just as the engine come to a halt, it's a different story.

I don't run into a great deal of water, normally, this last winter notwithstanding, but I see plenty of the finest dust imagineable, and there is none in the top end of the breathers on either of my bikes.

But, there's another way to break the vacuum in the breather. Run a T in the small vent that runs between the oil tank and the cam box, and run that smaller line to the airbox. It's neater, and will give the engine a big enough extra vent to keep it from building enough vacuum in the main breather to raise a column of water or mud all the way to the engine.

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grayracer, that's the best idea I've heard yet! I really hate having that big ugly hose running down the front of the frame, I wish I was brave enough to just pull it off, plug the nipple on the head, and vent it like you have suggested, but I think I'll just vent the smaller line to the airbox and leave the big ugly line be. Thanks for the tip! :)

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grayracer, that's the best idea I've heard yet! I really hate having that big ugly hose running down the front of the frame, I wish I was brave enough to just pull it off, plug the nipple on the head, and vent it like you have suggested, but I think I'll just vent the smaller line to the airbox and leave the big ugly line be. Thanks for the tip! :)
Wait a second! You need the big ugly hose!

The suggestion I made is only as a way to prevent the breather picking up water if submerged. The smaller 1/4" hose is in no way large enough to serve as the main crankcase breather. That has to be there someplace or other. Remember that your engine displaces 426cc Below the piston as well as above it, and the pressure that creates needs to be relieved.

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grayracer, I understood what you said, I just wish that it was possible to get rid of the big ugly hose. I'm going to try and do this mod real soon, and I'll post some pics when I get it done.

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