I usually use motor oil diluted in petrol but recently changed my technique: I pushed a piece of silicone tubing over the botton of the cable and fastened it around the cable outer casing with a zip tie. I then sucked on the silicone tube and dribbled 20W-50 on the cable at the perch end and was very surprised how quickly I got the oil sucked all the way through the cable.
Also, avoid bends in the cable. In the diagram above (Entry 34) I found the indicated cable route results in a very tight clutch. Instead of this I have the cable pass between the left carb and its air box, as per the diagram, and tuck behind the petrol cock running up to the frame where it is zip tied. The cable follows the left side of the frame and exits between the headlignt and left pigs ear and curves gently up to the perch.
Also, avoid bends in the cable. In the diagram above (Entry 34) I found the indicated cable route results in a very tight clutch. Instead of this I have the cable pass between the left carb and its air box, as per the diagram, and tuck behind the petrol cock running up to the frame where it is zip tied. The cable follows the left side of the frame and exits between the headlignt and left pigs ear and curves gently up to the perch.