Yesterday I was out in the shop.  Changing the clutch side gasket.  Little red 80 dribbles a little oil.  So all is well til I put the pump back on and start making sure it’s bled and we got oil.
nothing.
i check the tube, pulling it off the pump.
nothing.
there is oil in the tank.
pull the line off the tank.  A drip or two.  What? It’s full!!
take off tank.  I discover it was like all gummed up.  Inside is a brass screen.  Clean the gunk. Drain the oil. Clean the tank real well with a little gas then carb cleaner.  Blow out.

put hose back on, oil in. Now we’re in business.  All good.
im kind of glad I did this gasket.  Had I not , I would not have known about the oil shortage.  

i don’t drive it much. I have toodled around the yard low rpm.   

have any of you ever heard of such a thing?

using yamalube in the tank…

 

Good catch! 
Yes, it's something I check on every "new to me bike" by removing the bleed screw on the pump and letting the oil flow...  If I know the bike has been sitting many years I flush the tank with new oil.  If flow is poor, then I disassemble like you did.

Twice now I've found foil seals from an oil bottle in the oil tank.

I never would have thought of it!!  
She ran like a champ after the minor procedure.  All is well: didn’t know they had a brass screen in em.

good to know!!

Luckily they don't flow much oil to the cylinder. Main thing is you found it in time. We had an outboard oil back in the 70's that one farmer in particular used in his farm AG100 & caused similar sludge in the oil tank & tank outlet. Was a premix oil dark purple in Color.