Steamy Pipes !!

Just got my 84 Gpz750 running and noticed smoke coming from the right header pipe #4 (lower part of the pipe) I thought oil might be dripping onto the pipe but the underside of the engine and the pipe is nice and dry, so the smoke is coming from inside the pipe.

On inital startup there's no smoke, but once the bike warms up it starts smoking and is really noticeable. Any ideas or suggestions?

What color is the smoke, and does it smell like burning oil?
How many miles are on the bike?
Any visible oil leaks elsewhere?
Do you know it's history - did the PO do frequent oil/filter changes and other periodic maintenance, or did he just run the piss out of it and add oil when it got low, etc?

My guess would be a leaky valve stem seal, and/or worn piston rings if it's an oil leak.
I'd suggest doing a compression check and a leakdown test to help locate the prob.