Crankcase breather

With the hose(s) removed, if any oil or oil mist comes out of the breather, and it often does, you'll make a mess all over the tops of your carbs. But, if you're OK with that, have at it. On some of the bikes I see around here, it would only be an improvement, lol.
 
That's fine. In fact, that's how the early '70s 650s did it, also many other bikes from that era, before the E.P.A. clamped down and made them plumb it into the airbox.

I get very little, if any, oil out of mine too so dirtying up the pods isn't an issue. They get plenty dirty on their own, being that they're hanging out in the open air. I like the idea of possibly adding a little extra oil to them occasionally from the breather to help keep them oiled.
 
I'm after the single outlet but there are currently none on eBay in the UK. So.....im thinking block off the right port and use the left port with tube attached and running down towards the chain.......is this ok?
 
Mostly, Yamaha kept changing the design inside, they all work but some are better than others. Never done a hard test but figure the later ones are best. Then again I use stock air boxes and feed the mist back into the cylinders, a little top end lube never hurt nothing...
 
I'm after the single outlet but there are currently none on eBay in the UK. So.....im thinking block off the right port and use the left port with tube attached and running down towards the chain.......is this ok?


G'day Paul,

Yup that is what I have done used 1/2" silicone hose very flexible. Cannot say as yet as to how it has worked out as have not started the engine so far think it will be cool & groovy.

GW
 
I was able to use (2)Mikes Reed PVC Valve mounted right behind the engine. They work great. Looks like the design has changed a bit but the new one should be able fit in the same space.
XS2 189.jpg
 
So here's a question, I slid out the 2 port splitter and have had the left port removed and welded shut so in effect it is now single port and facing downwards, I'll take some hose and run it towards the chain.

Do I now remove the small piece of rubber pipe that sat inside the port (the one that reduces the size) or should I keep it there? I'm thinking it should now be removed?

Also, as I've kept the stock baffle plates etc do I still need an inline non return valve? I'm thinking I don't.

Paul
 
That's hard to say. I would think the hole in the rubber plug should be a little bigger because you're down to one pipe now, but maybe not as big as it would be by removing the plug. Maybe someone with a later factory single pipe breather could check the hole size on that for you?

Normally, your breather breaths in and out as the pistons move up and down. The check valve is a one way valve that lets pressure out but not back in. That creates a small vacuum in the crankcase and that's supposed to be beneficial for a couple reasons. First, the engine is supposed to make a bit more power like that. Second, that slight negative pressure can help prevent oil leaks and possibly alleviate minor ones you may already have.

Many of us who run pods use a short length of hose and locate the check valve above the pod filter. If any oil or oil mist does come out, it will just get recycled through the engine. This sort of mimics the factory set-up of having the breather hoses fed into the airbox. I had no clearance issues setting this up and in fact, it uses less hose and takes up less space than the factory set-up. This was my original set-up when I still had K&N pods .....

FrITjdS.jpg


I have since switched to UNI foam pods because the K&Ns don't work well with our CV carbs. The check valve set-up remains the same. I notice you have the K&N pleated type pods. They will cause you carb tuning difficulties.
 
I forgot to mention, we use the check valves with the baffle plates still installed. Don't gut your unit, that would let more oil out. The valves we use are power brake check valves. An engine PCV valve won't work. It can't react (open and close) quickly enough to keep up with the engine pulses.

NM4t1Dh.jpg
 
I have one off a n 82 on my 75. The hose that fits it is just the right size for the Brake check valve. The other side of the check valve is for a 3/8 inch hose. I have this hose run down behind the engine and off to the left. Any oil drips won't get on the tire.
I think I'll take the hose off and turn the valve so it drips onto the foam filter as 5twins recommends.
the hoe in the later breather is only about 3/16 inch or so. I read somewhere to drill it out. I don't think it made any difference when using the check valve.
From what I've read the better performance come from the negative pressure/vacuum the check valve creates help the rings seal better, thus a slight increase in compression.
Leo
 
PCV, not pvc. Positive Crankcase Ventilation. (Not poly vinyl chloride)
Sorry, just had to :)

Also, I do believe any PCV/ check valve should be as close to the engine as possible for best function. A reed valve, like the MikesXS one, integrated in a replacement breather would be perfect.
Finally, a reed valve type PCV should have no problem reacting fast enough for keeping up with an XS crankcase pressure variations. Reed valves are commonly used in 12 000 rpm two-stroke engines. If one really wants the optimal, fast reacting PCV reed valve, a thin carbon fiber reed should do the trick.
 
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Why was the crankcase breather connected to vacuum? I see many people running their breather to atmosphere and catching the oil mist using filters, but why wasn't it just done like this from factory? Is it because of emissions? Or is it because its more efficient?

Vacuum is strongest at idle and that's when crankcase pressures are low, so it makes sense to have vacuum assistance at low rpms. When venting to atmosphere, the breather is only really effective at higher RPMs.. do I have that right?

Should I care about venting with vacuum? or just vent to atmosphere and melt the ice caps.

Thanks
 
Why was the crankcase breather connected to vacuum? I see many people running their breather to atmosphere and catching the oil mist using filters, but why wasn't it just done like this from factory? Is it because of emissions? Or is it because its more efficient?

Vacuum is strongest at idle and that's when crankcase pressures are low, so it makes sense to have vacuum assistance at low rpms. When venting to atmosphere, the breather is only really effective at higher RPMs.. do I have that right?

Should I care about venting with vacuum? or just vent to atmosphere and melt the ice caps.

Thanks
well vacuum is tricky cuz it'll change your air fuel mixture (make it lean)
 
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