Rather than repeat the fountain, I put a pipe on it, ran it into a container and videoed the weirdness...
(it's a 360 video, you can move the mouse to look around - like at the oily water dripping off the ceiling)
So the fountain happened both times I ran it, and the stuff that came out looked like watery oil rather than oil with some water in it. Next step: drain the oil...
... which looks like water. That's not good, and it's something I've never seen before. Why on earth would anyone ever put water or coolant in an engine like that?
I've done head gaskets on cars before and I'm pretty familiar with the consequences of oil mixing with coolant. It usually goes both ways (oil gets in the coolant, coolant gets in the oil, but the coolant looks brand new and the level is good. When running there is no bubbling in the coolant overflow (usually a running engine will force gas and oil back into the coolant reservoir if there is a blown head gasket). As amazing as this sounds, I think the idiot who owned this before me filled the engine with coolant instead of oil, but I really can't understand why. It's either gross incompetence or he sold me a bike with a known blown engine, which is a pretty shitty thing to do. Incompetent or nasty, not a great set of choices there.
My first sports bike has been a bit more baffling than the XS1100 (air cooled, nothing weird there other than the ownership) and the Concours sports tourer which had been through hell, but was owned by a guy who knew what he was doing.
The muppet who owned this bike before me will have me going top to bottom on it before I get it out on the road - I can't trust anything that was done to it.
Follow up: the engine was full of gasoline because the petcock that portions fuel out of the gas tank had failed, causing the gasoline to run into the carbs, fill up the bowls and then dribble down the intake manifold into the cylinders, where it ran down into the engine. This is evidently not uncommon on motorcycles because of the way they carry their fuel above the engine. A new petcock, a carb rebuild and a couple of engine flushes and the 'Blade rides again. Point to remember: check for leaking petcocks on older bikes!
