Hi all. Carried out a service on the 1400 California. I found the airbox about half full of engine oil. Drained and cleaned the airbox and fitted new air filter. Filled sump with new oil and started the engine. Checked oil level on the dipstick and filled to just below the maximum. The measurement was taken with the dipstick full screwed in. I have since run the bike on short journeys with no problem. Now on a long trip and after covering about 600 Kms noticed an oil build up the the airbox drain pipe. I drained off about 100ml. Checked the oil level using the dipstick and it had dropped to about halfway between min and max level markings. I then rode about another 500 Kms and there is oil all over the left hand side of the bike and the oil level on the dipstick is at minimum on the dipstick. I suspect the oil is collecting in the breather box and for some reason is not returning to the dump via the drain pipe but instead is building up in the breather box and then draining onto the air box via the pressure equalising pipe. I think I may have inadvertently pulled the airbox drain pipe off the airbox when draining it last night hence the oil on the left hand side of the bike today. I will check that tonight. I initially thought the problem was that the sump was overfilled but that no I’m thinking that the drain on the breather collector box is blocked, twisted or kinked and it not allowing the oil condensate to return to the sump. Has anyone out there had a similar problem and if so what was the cause?? Many thanks Phil
The big block engines do not like being filled with oil to the max mark.
Each engine is a bit different but if overfilled they whip up a heavy froth of oil vapour which air pressure pumps up to the ‘oil separator’ where the oil is meant to settle and drain back to the sump whilst blow by vents to the airbox. Because the vapour and froth is so heavy a lot of that goes to the airbox where it pools and is drawn into the air inlet. On the injection models this can become a big problem as the oily gunk blocks airways in the throttle bodies 
making throttle setting almost impossible.
The problem can be worse in winter because a lot of the big-blocks are over cooled and on short runs they build up a ‘mayonnaise’ of oil and water-based combustion by-products which slows the drainage of oil form the separator. Obviously you do also need to check integrity of all the tubes to and from the oil separator, but also the usual advice is not to fill with oil above the halfway mark on the dipstick and then see where the level settles. Unless you have an oil leak it should stay above or at the minimum mark.