breather mod for 08 yzf 450

I recently picked up a 08 yzf 450, and I have been reading about the mud sucking issue for yamaha four strokes quite a bit lately, and since i ride lots of harescrambles and trails riding (often muddy) i would like to know if the problem still applies to the 08 yzf 450, or did yamaha fix it somehow? if it is necessary, which method is the best? also what are some other prudent modification a woods rider needs to be aware of for an 08 450?

Anything that puts a T in the line coming from the head, with the main vent in its current location and a second branch up away from water, mud, etc., will avoid the problem.

alright that sounds like ill need a kit for that, but ill just search it, thanks

Here's what I did. I went down to the local irrigation store and bought an inline T and screwable endcap that would work for the inner diameter of the breather tube. I then rerouted the tube to the top of the airbox and cut a hole where it made sense right above the midpipe/silencer joint. I put in the T and put a small chunk of tube down to a threaded cap. If/when I need to drain this, I just unscrew the cap. Hopefully this makes sense. It cost me very little and seems to do the trick.

the t that runs down with the threaded cap is in case oil decides to puke up your breather tube right? wouldnt it just bypass that if it was coming fast enough?

Doesn't the system you wanna put on need to have a check valve on the lower tube?

Am i correct in saying all you need to do is put a T piece near the top of the original breather tube, Than run the T piece into the airbox or next to it.

Therefore, on normal operation it is draining to the bottom because thats the easiest path to follow (may still get some oil residue in the top hose from oil vapors?) and if you were to get stuck in water so the bottom hose is covered it would than draw air through the top hose because thats the path of least resistance?

or am i missing something completely? im pretty sure thats how my old xr400 was set up from factory but could be wrong

Am i correct in saying all you need to do is put a T piece near the top of the original breather tube, Than run the T piece into the airbox or next to it.

Therefore, on normal operation it is draining to the bottom because thats the easiest path to follow (may still get some oil residue in the top hose from oil vapors?) and if you were to get stuck in water so the bottom hose is covered it would than draw air through the top hose because thats the path of least resistance?

You are correct, yes. The two things that would make the system ideal would be a reed type check at the bottom (allowing outflow only) and a filter of some sort on the top branch. Neither of these is strictly needed. With a T'd line, there would never be enough vacuum to raise water into the engine because the air flowing in through the top branch would prevent it from building that high.
Am i correct in saying all you need to do is put a T piece near the top of the original breather tube, Than run the T piece into the airbox or next to it.

Therefore, on normal operation it is draining to the bottom because thats the easiest path to follow (may still get some oil residue in the top hose from oil vapors?) and if you were to get stuck in water so the bottom hose is covered it would than draw air through the top hose because thats the path of least resistance?

or am i missing something completely? im pretty sure thats how my old xr400 was set up from factory but could be wrong

yeah that sounds like it makes a lot of sense.. but does the 2nd hose need to go to the airbox? couldnt you just zip tie it to the frame up high or something?

One last question, if i were to ride the bike as it is completely stock through water that is completely covering the bottom hose would it suck water in even if i didn't stall it in the water or try start it in the water?

yeah that sounds like it makes a lot of sense.. but does the 2nd hose need to go to the airbox? couldnt you just zip tie it to the frame up high or something?

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To my understanding it is not necessary to put in the airbox, again someone correct me if im wrong

Mine doesn't!

I have been running that risk as I have been only riding stuff I know really well and have been riding for years. I am doing my first Enduro on April 11th so I am gonna do the mod soon.

One last question, if i were to ride the bike as it is completely stock through water that is completely covering the bottom hose would it suck water in even if i didn't stall it in the water or try start it in the water?

To my understanding it is not necessary to put in the airbox, again someone correct me if im wrong

No it wouldnt suck water in the stock bottom hose unless you stalled it or tried to kick it over.

i wouldnt think either of the hoses would need to be filtered because it comes stock with the hose hanging down in plain view without a filter.

One last question, if i were to ride the bike as it is completely stock through water that is completely covering the bottom hose would it suck water in even if i didn't stall it in the water or try start it in the water?
No, not necessarily. It could under some conditions, but usually not.

The breather is there for two reasons:

  1. To relieve the pressure created by the underside of the downward traveling piston and the vacuum caused by the upward traveling piston. This is obviously a zero sum event in itself. One thing cancels out the other, and no more will be blown out than taken in, or vice-versa. It also happens at a high rate of speed, so because of the fact that air is both compressible and expandable, there is normally not enough time on a single upstroke to pull water up the entire length of the breather tube before the pressure reverses and it gets blown back to where it was.
  2. To relieve the pressure created by oil vapors and combustion gases that leak past the rings. This one is an outflow only game.

So we have a net outflow under normal conditions. Just keep it running.

Excellent, thanks for clearing that up

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