working on a double 8 steel right now but for grins and giggles, when a break comes, i will measure oil bag pressure. however, with the newer info mr. hippy put out about the holes in the upper cam cavity, i do not expect to see much diff, but mine does not have them so numbers probably be diff.
testing with a vacuum on the checks is more comprehensive than pressure.

Only conjecture at this point AFAIK. I (and maybe others in the past) have postulated a theory that if you have some kind of problem which causes oil puking, then larger breather holes could exacerbate the problem. Either due to a) weak umbrellas allowing more air back IN the larger hole; or due to b) other ways for excessive air to get IN (leaks, blowby).

In either case, air out-flow is too much and the oil separator (at the breather) doesn't drop out the oil fast enough.

In the case of "b" the larger hole may actually be advantageous for other reasons - mainly lowering CC pressure which would otherwise be too high with restricted breather bolts.

Now, as to whether the higher outflow is "normal" for a given build and larger holes (or some other workaround) is necessary vs being just a bandaid, that appears to be situation-specific. It would be nice to have a straightforward way to determine which venting mod is best - weighing out oil catchcan etc, vs. more restrictive holes. IMHO this starts with measuring actual CC pressure and/or breather flow.

(Keeping in mind that oil-puking has other possible causes, too)

I think one common factor is engine upgrades.
The addition of bigger pistons would seem to create higher volume / more pressure than the little bolt hole.
Then the aftermarket holes being bigger should lower the positive CC pressure some... maybe even closer to what the MoCo intended to begin with.
Lowering positive also lowers negative by cause and affect.
CC pressure was raised in the interest of better scavenging.
(to keep the oil against the sump scavenge port and moving out)
No matter the oil pump you have, the oil has to be there in order for the pump to pick it up.
So changing to the bigger bolt hole isn't necessarily a bad thing but testing should be done to see what the actual affects are and what the changes did to the pressure.

I don't think moving the vents out of the A/C stopped or started puking.
But oil puking out and dripping are different conditions.
The significance of the breather bolt hole size is that it changed the pressure inside.
I believe there are several ways to change the pressure playing around with the vent / lines.
I believe a longer breather vent hose adds restriction, as does several loops, a catch can, a filter on the end and others.
So six in one hand, half a dozen in the other..

woops, dieselvette beat me to it.
Told you I type slow. :doh

30 psi as a relief or as mean oil pressure (which would be twice as much oil in the sump than OEM (except XRs).

Oil Pressure from the pump:
1992-2004
7-12 psi idle, 10-17 psi (2500 rpm)
2013 XR1200X
16-20 psi, idle 40-44 psi normal riding

Deimus' first mod was a vent from the oil tank itself.
His second mod was the breather in the vent line to the cam chest.
But that didn't work either for him.
Others had said they were still using it.
http://sportsterpedia.com/doku.php/t..._the_cam_chest
http://sportsterpedia.com/lib/exe/fe..._by_deimus.jpg

86-91 engines have a 30-35 psi relief built into the filter pad.
This should only open at startup and instances where the filter clogs up.
But it has a habit of opening more than that and even staying open in some instances.
http://sportsterpedia.com/lib/exe/fe...hippysmack.jpg

http://sportsterpedia.com/lib/exe/fe..._annotated.jpg

I seem to remember them thinking 30-35psi. Whoever it was tested the stock oil pressure before coming to that conclusion if I recall.

Hippy - you are wise to distinguish oil puking vs oil dripping. I had been saying oil puking sometimes when I actually mean dripping. (Maybe i'll go back and edit those posts).

That being said, ive never had either condition. But I have seen wetsumping. Given what I know at this time, it was caused by either high CC pressure (blaming blowby and/or restricted breathers) or high oil level, or inadequate sump pumping. Or a combo all-of-the-above. Or different things at different times.

So if I was asked by some random Joe how to diagnose their wetsumping and fix it on a budget: start with patience first, and only address one problem at a time. Don't go directly to a shop, but instead start with the vital signs that anyone can check. Whatever you do, DON'T start with breather mods. And don't get all excited about a mess of oil out the breathers, or running oil level a little lower than you're used to, just clean it up and carry on in the right order.

The first step would ensuring that you are running oil level below half, and follow specific level-check procedure and re-fill procedure at oil change. (Remembering that even a shop could get this wrong). Next, make sure you know what are the signs of wetsumping , and then Put on several hundred miles, or until you establish a pattern. If that didn't fix it, Only then can you move to the next diagnostic, which is...?

Yes, i also should have said dripping and not puking!
I have only ever seen 1 drop of water and a trace of oil from my vent hose, so i think mine is all good.
I'll keep watch and see what/when if anything changes.
The only thing you don't have with modded airbox venting is the vacuum that would be in the stock set up.(probably been covered/discussed already).

Why does oil 'drip' from the vent?
Matter of fact, why does oil 'drip' from ALL Sportsters whether out the vent or in the A/C?

Yep, you're about to step into an oil thread. :D
That would mean that all our engines have the same HP, same parts, same blowby, same mods, same paint, same oil....:sofa

OK, you guys are killing me on this idea of running the oil at half level or less.
Please explain why this is necessary.
I've explained why I feel this is un-necessary and that it is a bandaid over the real problem.
To me it's like saying, if it squeaks, drown it with WD-40 and forget about it.
I'd like to understand how this practice got mainstream.

I'd think the diagnostics start with the breather valve / umbrellas.
That is the lock on the door. If it opens by itself, check the lock.
How do we test the umbrella?

edit: Anybody got a Durameter and a few new and old umbrellas.

diesel, you've mentioned that the umbrella can be less pliable and still work although with a possibility of increasing back pressure.
We know 91+ breathers have the drainback hole on the vent side of the umbrella.
So blowing thru it from the outside doesn't tell you much about the health of the umbrella unless the air you can pass thru it is excessive.
Functionality wise, I see no need to replace them if they are still working.
So what's the criteria other than so you won't have to do it later (which can get expensive depending on how much that fact works on your brain).

edit:
I take that back too.
The first step is diagnosing what, when, where, how fast or slow, at startup or during normal riding, only during wheelys, or only on Tuesdays etc. etc. etc.