FAO Grayracer - Oil breather mod

The washer on your air filter element bolt is upside down, BTW. :p

:lol: Oops, I'll fix mine next time too. Thanks!

I ride only on flat dirt roads. Can I leave the stock system?

Mine is stock, as issued, as is my son's, as were the two YZF's that went before those. We ride some MX, some trails ranging from fire roads to Black Diamond, and a lot of desert, including dunes. We have had no trouble whatsoever. We see very little water, however.

Where is everyone getting that K&N filter? And what part # for it? I will need to do this mod over winter and am interested getting parts lined up now. Thanks.

After looking at all the mod options, I am going with the Yamaha fix kit here;

http://www.thumpertalk.com/forum/showthread.php?p=4956573#post4956573

http://www.thumpertalk.com/forum/attachment.php?attachmentid=5372&d=1187932471

Makes the best sense to me. Provides filtered air to the head. Keeps water out. Traps excess oil from overfills. I checked my 04 WR450F and my intake boot has the adapter port molded in ready to be drilled out. Why hasn't Yamaha done this from the factory ?

Because it blows crankcase vapors and oil directly into the intake side of the air filter.

What they did on the WR is essentilally what Jones has done.

*Update* Found a major design flaw in my modification. Down to me not thinking ahead, I forgot that the T part may interfer with the exhaust. Which it does....back to the drawing board. See pics below, I have had to run the lower tube round the front of the bottom of the carb, it was the only way I could think of, it is secured in place by the white ziptie you can see around the intake. Hopefully this will be ok.

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You can see the zip tie etc in this photo and the way I have had to route it to avoid it touching the pipe.

Image012-1.jpg

I have had to run it on the other side of the shock, it rubs it slightly but ive bounced up and down on the bike and it dosen't seem to cause any major interference issues.

Image014.jpg

Here it is poking/dangling out of the bottom, this seemed the most logical way to route it.

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I'm planning on doing this mod to my YZ but I don't see the need for the K&N filter on the end of the breather line in the airbox. If it's for dust, the stock system on a YZ doesn't deem it nessesary so why bother?

Let me ask, I thought that the reason for relocating the breather hose was to keep it up as high so that it would eliminate the potential for sucking up trash or dirt backward through the breather hose and getting stuff into the engine.

If you run the breather down under the bike you still have the potential for the problem. Also most things would flow the path of least resistance, so with the filter on the other end, thus restricting the flow of air, would seem to me that it would suck from the breather tube located in the new position. Doesn't make much sense to me. Why not run a "Y" and run both tubes into the breather box with two foam filter inserts. It would seem that it would eliminate any potential problem, sucking up stuff from down low on the bike.

Let me ask, I thought that the reason for relocating the breather hose was to keep it up as high so that it would eliminate the potential for sucking up trash or dirt backward through the breather hose and getting stuff into the engine.

If you run the breather down under the bike you still have the potential for the problem. Also most things would flow the path of least resistance, so with the filter on the other end, thus restricting the flow of air, would seem to me that it would suck from the breather tube located in the new position. Doesn't make much sense to me. Why not run a "Y" and run both tubes into the breather box with two foam filter inserts. It would seem that it would eliminate any potential problem, sucking up stuff from down low on the bike.

I think water would provide more resistance than the filter. Mike

I think water would provide more resistance than the filter. Mike
As long as the filter was at least reasonably clean, that would be true. However, it only takes a 1 in/hg vacuum to raise water 13", so the filter needs to be checked and maintained, or left out.

As to why it would be used at all, the air box is a somewhat dustier environment at times than the outside air is, and the run of hose back to the engine itself is shorter from that point. Then again, one could simply place a filter on both outlets for balance.

I think water would provide more resistance than the filter. Mike

True, but if we were just talking dirt, it would suck up just as the stock set up. In my opinion it would be best to run the hoses up towards the front of the bike or under the gas tank, up high. This way you would help limit the potential of sucking up water. Also as Grey states with the check valve style flap incorporated into the system and a lightweight foam filter that you could oil, may perform better than the bulky filter mounted in the airbox. I'm not knocking the modified breather system, but just voicing my opinion.

How about this then;

Since a filter isn't really nessesary unless you're in the airbox's dirty environment and since water will take the path of least resistance and because you want to keep the line's exit down low so oil won't drip down your engine...why not just leave the stock YZ configuration in place with the addition of a T and 3" of new line coming off the top of the exsisting breather line up under the tank?

That way (1) it looks stock, nothing wrong with that. (2) it now has an alternative port when the OEM line's under water. (3) no oil dripping anywhere but below the bike. (4) no line squeezed beside the shock that will eventually wear through.

The main reason to run the line to the air box is so that in the event that it does blow oil out that end, it goes somewhere where it isn't an issue. If you put it under the tank, and it never pukes on anything, it isn't a problem.

I have a check valve from thumper racing that I just sliced in to the breather line on my 08 450f. Does this accomplish the same thing i guess right?

they call it a case vent see here:

http://www.thumperstore.com/Case_Vent_4_stroke_Motorcycles_and_ATV_s_p/roughhouse_case_vent.htm

I had it on my ktm, and switched it over when i got my yz.

On a similar topic, where are you guys routing your carb vent hoses? Does anyone use a filter on them?

thanks,

Ralph

$70?? I'm in the wrong line of work.

Anyway, locate the two vent lines that exit the float chamber pointing straight up and route them to either the air box or up under the tank. Some run filters on them, I don't. The only time there is a steady, continuous vacuum applied to these hoses is when running the "choke". Air for that circuit comes from the float bowl, and must enter through the vent lines. (bad design)

Think of the mess to deal with when you have to take off the carb.

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