Way back in the day I had a 73 Superglide.
Parts were hard to come by so I had to make do. Also money was real tight. Still is.

The oil filter and the gasket for the cap were one thing I had to self help.
I ran 60 weight avaiation oil in the summer and 20-50 in the winter. Mostly Penzoil.

The oil flowing back to the top of that oil tank inlet going into the filter was foamey --always. And I managed to get it all over things a time or two. Pissed the wife a time or two. Homemade gaskets.

If oil is coming back it has to be going in. Its a loop. Thats a pure fact.
Must go thru the filter to get into the tank.
All that churning causes foam coming out of the engine. I would thing this is natural.
This is a dry sump type system. Actually this is a real good thing.

The oil going into the engine is settled and the air ia seperated out in the tank
Oil going into the engine from the bottom of the tank has much less air entrained, after settling, than the oil going into the tank top,-- that you see.

Also the pressure in the oil tank, from the scavenage pump discharge, doesn't let the air bubble so much in real life.

This assumes the vent system is all OK. I used to run that outlet down to the drive chain and let it breath on that thing.
Chain and sprokets lasted a long time but that was another thing used to **** the wife.

 

Thanks for the replies. rh8234 i did get that address, thanks my friend..............................No this is the same oil i have been useing. Valvoline 50wt racing oil and i cant ever remember ever seeing it foam like that before. Old gunny, i agree about the oil making the loop through the filter because it is returning to the tank. There are a couple of things i probably should have mentioned also. My bike has been stored for about 3 years. I just started riding it again about a month ago. I have noticed that it is leaking alot of oil since i started riding it again. Im having trouble locating an exact source for the leak.I have check all the oil lines i could get to and made sure they were tight. Also made sure primary and all other screws are tight. It almost seems like the motor might be building more presure than it should and causing leaks. I checked for vacume in the primary and it did not register any. I guess that could be caused by a leak some where.

 

I've noticed the same thing on occasion .. I always thought it had more to do with being overheated ... not from being cold with moisture in the tank. I think the only time I ever noticed it, was after being stuck in traffic on a hot day (after riding for hours..so it's not cold at all) So hot, as a matter of fact that it's after my bike goes into heat management mode.

It may very well happen more often than that and just be coincidental that that's the time I checked my oil and saw that. HMMPPFF! Now I am more confused that before.

 

First thing I thought is blow-by of the piston rings. Not having ridden it for three years will dry out the gaskets and give you leaks in many places. Sitting is harder then riding and maybe the rings have siezed to the piston and are not sealing the combustion pressure too well. It may start and run OK, but is blowing your oil into foam. I, myself, am a believer in Kendall motorcycle oil. It seems to cling to the cylinder wall and stops 'dry start-ups'.
I can't remember what oil I was using at the time, but when I noticed foaming in my Shovel, I changed to Kendall and the problem went away. But it was a clue to the worn piston to cylinder clearence. The next year I went to Daytona and the engine wound up trashed. (Thirteen years with out the best of oil changes and a year after bead blasting which wasn't cleaned out as well as it should have been.) The rod bearing separators wound up in the oil tank little pieces at a time. The pistons hit the flywheel and broke off pieces and it all went through the engine and oil pump. The engine didn't lock up but got me to a gas station where I hitched a ride for me and the bike back to Ormond Beach. I can't really say the oil is why it didn't lock up, but it should have stopped running.
Anyway you need to check your compression and pull a leak down test to see if that is your foam issue. Foamy oil is not as good for the life of the engine.