My 89 UC has never done it. I ride it all summer and never let it set in the winter more than 2 weeks without letting it warm up completely.

You don't need a filter on the bottom of the vent hose, just leave it open and hanging down under the bike 3 inches or so. I ran mine through the right hole in the cross member. (Zip tied it there) That's where it hangs down from. (Oil will drip from there after a ride) If it sumps it will do it under the bike and not out the air cleaner. Don't over fill the oil, that contributes to the problem along with letting it set.

 

Thanks guys. I started it today without the air filter in place and not one drop oil from that line.

 

Still need to vent it to the atmosphere.

 

 

That line won't leak after only one day.
As previously mentioned vent that line to atmosphere and cap the hole in the air cleaner.

 

Discussed here before. Manual gives clear instructions to prevent this after sitting for awhile, like over the winter. Involves removing oil line and plugging line and connection on oil pump. Only takes a few minutes. Been doing it on my '87 Heritage since new. Never pukes unless I forget to do it. I have once or twice.

 

 

The other thing is this. While the motor is running during riding oil is very lightly misted into the carb. The mist is sucked into the carb and the combustion chamber. Misting oil is "supposed" to be burned off. Over time that may build carbon especially if the misting should increase. Not to mention gunk up the carburetor. Is your carb black in the throat?