This is where I'll hop aboard the thread. Thanks James for some good questions.. This is a case for me where the forum search worked as intended. I don't often look around the small six forums.
I am using a 300 six, with a single advance DII dizzy. The advance unit is toast, but I do have another donor dizzy that has a dual advance unit.
With my vacuum pump, i confirmed the earlier post about the top port retarding timing, while the normal front one advanced it. Are the stock vacuum advance diaphragms adjustable via the allan key method?
As James asked, I am also wondering if any effort need be made to plug the top port.
Further, there seems to be conflicting information about vacuum source. Borte, you state manifold vacuum is the way to go, but wont that give a higher advance at idle? Why no ported? Wondering if there are pros and cons to both.
In my situation, I run propane, which needs a lower total advance, all in at an earlier RPM. Thinking that using manifold vacuum for the advance would allow me to use a lower static advance -thus providing a lower total advance artificially before recurving a gas dizzy to give me something closer towhat I need-.
I realize the last question/point is threatening a partial hijack of the thread, but all additional information is good for reference and for all of our knowledge base, right?
Thanks
