WET SUMPING
One common problem that scares the hell of of people is wet sumping. This is basically when you have too much oil in the bottom of the crankcase and it either blows out the breather or the flywheels throws it up on to the piston skirts and the motor smokes like hell or both.

There are a couple of things that will cause this. Most of the time it is because of a check valve in the oil pump that is not seated This is very common in Harley Sportsters built before 1977 and softails fall into this group ocasionally, Triumph Twins, and early Norton Commandos are known for this also. Usually this happens after the bike sits for a couple months. On the Sportster it usually blows a big puddle of oil out of the breather tube attached to the bottom of the cam cover. Sometimes it will smoke, sometimes not, it just depends how much oil is in the bottom of the motor. Usually if the plugs don't foul, it will clear itself out just by running the motor awhile. If it happens repeatedly at shorter and shorter intervals it is probably time for a new oil pump or ap least a rebuild.


Source: http://raskcycle.com/techtip/webdoc8.html#WET%20SUMPING