Tiger cub first start in 48 years

I have just had a 1955 cub going for the first time since 1978. I changed all the oils and cleaned the oil tank out a couple of months ago. All the oil had drained from the tank but wasn’t in the crankcase. The engine is smoking badly from the exhaust. I just run the engine for about a minute. I couldn’t see any oil returning to the tank. The engine actually sounds quite good, with no rattles.
It’s not my bike so I have no history.
Any ideas please.