I replaced the old, worn-out pump in the Sonoma with another old, worn-out pump, and have had this question on my mind every time I set the pump timing, and finally thought to ask someone.
On all 3 engines I have, at the 15? mark, there are actually 2 marks there. They are far enough apart to make a difference on the dial gauge when setting, so I usually use the first one to come up. So my query is Why are there 2 marks very close together, and which is the correct one to use?

The first pump wouldn't allow me to turn the pump up any without idling too high, and this one allows me to turn it up so it smokes a bit more and idle, but it idles so low when cold, even with the high-idle set and on, I don't know how it keeps running. So it looks like I may put the original old, worn-out pump back on. No noticeable power gain anyway. I'd rather it idled better cold.
Been looking at converting a newer truck in better shape anyway. Well, 1995 newer at least. Gotta use that last engine in something. <img src="/forums/images/graemlins/cyclops.gif" alt="" />