I agree with rockhopper.
Oil capacity of a 748 BP is 3.5 litres. You probably won't get quite that much in, but that's the sort of amount you should have available. Put the bike on the paddock stand and fill it until oil fills the sight glass. Replace the oil filler cap. Start it up, and make sure the red oil light goes out straightaway (if you have one, unlike me
). The oil level in the sight glass will drop. Stop the engine. Fill it up until the oil reaches the top line. Restart the engine and re-check the oil level.
And check the sump filter, as Demon says.