Back in the day. The Hardly Ableson riders used Kendal GP -1 70 weight racing oil in my neck of the woods. It was thick as molasses in January in Maine. I had an old Honda 400 two banger. I put it in in the summer. My first experience with synthetics was in the early 90's. I put Mobil 1 15w-50 in a 1981 Yammer Hammer 550 Seca. Thing ran like a hamster on crack. Only problem was the wet clutch didn't like it. It never slipped. But the clutch friction disc would stick to the steel disc at cold start.