No the carburetor can't create any vacuum. The piston are when returning down the barrels after closing the exhaust valve. The blowby theory should work the other way around too by pulling the oil up past the rings but I have no blue smoke what so ever.

Ken,

How much would you say that it is excessive vacuum?

I face the same oil sump filling problem.

Interesting. What breather are you using? New or old? Original or reproduction?

It's the original style but was refurbished according to Sean's instructions.
viewtopic.php?f=7&t=4333

Viking,
is it the hose between the air filter and the carburettor which you've disconnected, as suggested by the statement that it will collapse inwards when fitted and the air filter inlet is blocked?

If that's the case, I'm not quite sure what you're driving at, as there's no direct link between vacuum in an engine's intake system and any vacuum produced in a crankcase by a breather valve...

ken

Is the small pipe between the filler and the dipstick tube clear? I had a problem a few years ago with so much oil being pumped into the air filter/atmosphere that the brakes wouldn't work properly due to over lubrication. I took the breather off, cleaned a load of hardened carbon deposits from the small outlet on the breather, and replaced the little bit of pipe, and it was fine again. It may just have been a coincidence, but I assumed that some oil condenses on the walls of the breather, and then drains back into the engine through that pipe.

No I don't disconnect the goose neck hose. Everything fitted per normal, I block the air intake ( big black hose on the housing) and the goose neck is sucked flat. Removing the hose breather/filter housing, the goose neck is no longer sucked flat.
I'm starting to think that the air filter I fitted (not foam type) may have to much restriction
reducing the air flow. When vacuum is created (in the barrels) the air is ''taken'' via the breather taking the oil with it. I will find a foam filter and connect back to normal to see what happens

It could be blocked, since all the paint inside is dissolving

Intake vacuum is present below the throttle butterfly valves, because of the effort it takes to suck air in, not in the air filter box. Crankcase vacuum is created by pistons moving outwards, previously expelling blowby gases etc. through a working one-way breather valve. I should think it is more of a problem with the boxer engine, as with inline engines, for example, there are no big changes in the crankcase volume, with pistons reflecting each other's movements etc. and keeping it farily constant. At least the 4 cylinder engine in my BX has a breather tube, but no valve in there.
Also the small amount of oil in the filter box is a common design feature of "wet" air cleaners, where the fast flowing air is forced to change direction above this oil puddle and heavier dirt particles simply "fall out" due to their greater inertia.

Saurus,
the 'quote' system must be playing up, as I most definitely did not write what's in that box in the post above.

ken
( Still wondering if this is an 8.5 or 9.0:1 engine and close to suggesting a leakdown test. )