[RGT]

I was poking around the bike the other day and I checked the oil and failed to lock down the oil reservoir cap/dipstick when done. Subsequently  I kciked over the engine and noticed that the oil reservoir cover popped up and reseated itself, reminding me to lock it down and pointing out to me that the duckbill vent arrangement on my bike is wholely inadequate(maybe the newer bikes and 500's have a better arrangement?)   This got me to thinking of past performance car engines I used to build and timker with and efforts then to not only vent the crankcase to eliminate pressure but also to reduce the pressure which does several things. It reduces the work the pistons have to do in countering it, leaving more power to propel the bike, it scavenges the unwanted vapors, which can break down the oil, and it allows the oil to settle in the crankcase faster, which should reduce any power losses due to the thick oil in these engines being dragged around the crankshaft.(trying to combat this windage effect of the oil carried around the spinning crankshaft was also done by installing plates within and engine around the crankshaft to block this airborn mass and sometimes by installing dry sump systems, which we already have).
Ace's excellent articles(Thank you), particularly his comments in his Cam Timing post regarding his efforts for making a streetable/useable power improvements have me wondering what has been done in the past in addressing the crankcase pressure.

[RGT]

To combat the crankcase pressure we can vent it, I see that Bunn has a system to do that. On car and truck engines they use intake vacuum to scavenge the fumes for engine longevity and emission's purposes. On race engines they would employ fittings in the header pipes connected by tubes to the engine for drawing out enough air to actually lower the pressure in the crankcase below atmospheric. I am curious what might have been done as I figure out what I may try on my bike, this bike design has been around for so long I am sure there have been all sorts of experimenting done.

[ace.cafe]

The duckbill system is the best.
It vents the fumes well, provides a partial vacuum in the crankcase, and the duckbill is the fastest reacting type of valve style(reed valve).

Plus, it's cheap.

Your bike is the old style breather elbow on the engine case left half under the cylinder, and that will do an excellent job.
Just put an appropriate size hose on it, and lead it on a continuous rise route up to around the seat area, and then route an exit where you like it, and put the duckbill on the end. I like to terminate mine at the back end of the bike.
Done.

There are a bunch of breather things out there, and IMO the plain long tube with duckbill is the best. You can spend more money, but I don't think you'll get any better results.  This is not to say that another type won't work, but that the bike came with what is a proper design to do the job, and it does everything a proper breather is supposed to do, and does it very well. Just use it with a longer hose, so that any fine oil mist out the duckbill exits out the back.

I use a transparent hose, so that I can see if anything is coming up the hose, especially that "mayonnaise" that sometimes occurs on cold days from water vapor condensing in the engine.

There is no need for any "exhaust suckers" or vacuum pumps, because this big single pumps itself down nicely all by itself in a short time. All it needs is that one-way duckbill on the end of the hose. No "breather tube oil returns" or anything like that is needed on a properly functioning Bullet.

[RGT]

I had not thought through that the pumping action of  a single cylinder, in a fairly closed system with the one-way duckbill exhausting the crankcase could actually achieve a partial vacuum. Thank you. yeah simpler is definately better. I will try the upsloping tube you describe as that should accomplish my other goal of having a cleaner bike. Do you actually get any oil out the end? or does it tend to stick to the tube wall and work its way back into the crankcase?

[ace.cafe]

I had not thought through that the pumping action of  a single cylinder, in a fairly closed system with the one-way duckbill exhausting the crankcase could actually achieve a partial vacuum. Thank you. yeah simpler is definately better. I will try the upsloping tube you describe as that should accomplish my other goal of having a cleaner bike. Do you actually get any oil out the end? or does it tend to stick to the tube wall and work its way back into the crankcase?

Any oil coming up the tube is generally in a fine mist. It may burp a bit if the oil level is high, but not much. The purpose of the upsloping tube is to provide a "stand-pipe" effect, so that any significant oil that may come out in a burp, or even much of the mist, lands on the tube walls on the upslope, and drains back down into the engine.
So. the only oil that ever makes it out the duckbill is minimal, and only the finest mist that is carried by the air.

In practice some fine mist will come out the end of the duckbill, and that is why I lead the hose to the back of the bike, so it exits where it will not get on my clothes or the tire. The rear of the bike has some swirling air currents there, so some oil mist will collect on the license plate and rear fender. But it is minor, and easily wipes off.
I don't find it objectionable, and I only wipe mine off every couple of weeks, it doesn't get much on there during a ride.

[UncleErnie]

If you haven't left the room yet-
I'm using a shorter tube that goes into a bottle to collect that stuff.  It does not go back into the engine, and it collects an ounce or 2 along the way.  It looks like chocolate milk for cryin out loud!  Why would I want that going back in my engine?

[RGT]

Uncle Ernie, do you still have the duckbill on the system?

[ace.cafe]

If you haven't left the room yet-
I'm using a shorter tube that goes into a bottle to collect that stuff.  It does not go back into the engine, and it collects an ounce or 2 along the way.  It looks like chocolate milk for cryin out loud!  Why would I want that going back in my engine?

Well Ernie, you could put it in a catch can if you like that better.
Nothing wrong with that.

But, the rest of the oil inside is mixed with water like that anyway, until the engine heats up and vaporizes it off. So, it's not "saving the engine" or anything like that.
The rest of the oil is contaminated wth water too, until it warms up.

[UncleErnie]

Oh.  Well, the bottle keeps oil off my tire, too.  That's the excuse I'll go with from now on.

Mr RGT, as per millions of posts here- I just glued (RTV silicone) the duckbill fron inside the catch-can to the end of my vent tube directly.  (Can't remember now if I turned the hose around now, or not...)  So- the crankcase and primary tubes both go into my little Coke bottle zip-tied to the frame. 
BTW, this would cost me a LOT of points in any bike show.  Not that I'd have many points to start with.  My wife is the only thing that still looks good after living with me.

(I shall eschew any smartypants addendums at this time.)

[scouse]

So as I understand it you can vent straight out from the crankcase to the back of the bike with a duck bill?
My 95 Bullet has the small can under the battery case and then vents to the air filter.
I plan on changing this and have it go into the can and then out the back to the license plate. Do I still need a duck bill?
I understand that I will need to drain the can once in a while I not sure how often because the bike is new to me and I havn't had it on the road yet.
If I do need a duck bill where can I get one from.

[Blltrdr]

So as I understand it you can vent straight out from the crankcase to the back of the bike with a duck bill?
My 95 Bullet has the small can under the battery case and then vents to the air filter.
I plan on changing this and have it go into the can and then out the back to the license plate. Do I still need a duck bill?
I understand that I will need to drain the can once in a while I not sure how often because the bike is new to me and I havn't had it on the road yet.
If I do need a duck bill where can I get one from.

You only need to run your breather hose to the back of your bike if you plan on terminating that hose at the end with a duckbill breather. I truly can't remember how the catch can on your bike looks internally because I threw mine in the dump bucket years ago. So I would probably suggest to update to the newer style type catch can and mount up high under seat if that is what you really want to do. Plug the extra pipes that you don't need, you could use the larger of them for a valved drain if you want. Run your breather hose from engine up to act as stand pipe and then to your can connection which has a duckbill inside the can. There is a vent pipe on top of the can lid. You could leave it alone or run a hose from it somewhere, just don't plug the vent. However you decide to do it make sure you run your hose up high right as it leaves the side case for that stand pipe effect. You could probably make your own catch can and save a few bucks. Mount it so it's easy to get at and maintain. There has been a lot written on this subject, you might do a forum search.

[ace.cafe]

So as I understand it you can vent straight out from the crankcase to the back of the bike with a duck bill?
My 95 Bullet has the small can under the battery case and then vents to the air filter.
I plan on changing this and have it go into the can and then out the back to the license plate. Do I still need a duck bill?
I understand that I will need to drain the can once in a while I not sure how often because the bike is new to me and I havn't had it on the road yet.
If I do need a duck bill where can I get one from.

The duckbill is  in your can,and if you look in there, you should see it.
It is on the end of the breather hose that comes from the engine, and that's where it needs to stay if you are going to continue to use the catch can.
You can run the hose that went to your air filter anywhere, Back of the bike, or wherever you want to run it. It can have an open end, because it's only the fume vent off the catch can. No duckbill or plug on that.

[bullethead63]

Like ACE,I replaced my black rubber hose with a clear vinyl one...I like to see that there's a little movement there when it's running...my bike had been sitting for seven years,so I've been replacing all of that cheap,crappy Indian rubber,one piece at a time...the battery straps were first,and one day I noticed a subtle "THUP-THUP-THUP" noise coming from my crankcase...my hose had split about 1 1/2",so I replaced it with clear vinyl,and stainless clamps...

[Geirskogul]

Pressure's so low you don't have to use clamps if you get 3/8" ID tubing.