[Charon]

You can feel the varnish in old gasoline. Stick your fingers in. And wait till it dries. Then touch your fingers together. You will feel a very slight stickiness. When you pull apart. Last year I had a guy stick 4 intake valves on a flat head v8 Ford. I doubt the system had 4 ounces of very goopy tar in the tank. It does not take much.