1982 kz750 (4 cylinder) burning oil

This is my first post here, and sorry if the topic has already been discussed, but I couldn't find it anywhere. I recently bought my first bike, a 1982 kz750e. I knew that it was leaking oil out from the head gasket when I bought it, knew I'd have replace it before I did much riding. I took it out for the first time today on about a 15 mile ride, and after it was warm enough I cracked the throttle open, and when I hit about 6k, it started smoking out the the exhaust like crazy. I'm talking clouds of white smoke billowing out. Anybody know what could be causing this? Any help is appreciated, thanks.

Is this before or after fixing the head gasket.

Before. I haven't touched the engine since I bought it.

Sounds like you need a top end rebuild. Once you get the engine apart measure everything and figure out what needs to be done

I would renew the valve stem seals,they do the hardest job of all seals.
They got hard as rock over the time by the heat and than pump oil over the valve stem into the combustion camber.