My vacuum advance doesn’t have a number stamped on the arm, but with the spec sheet that came with the distributor it says the vacuum advance adds 15 degrees at 18-20hg of vacuum.
I’ve already turned the adjuster screw ccw a couple of turns and at the moment I have it to where it’s adding 11 degrees at 18-20hg.
But the issue is when I’m crushing down the highway in overdrive the vacuum increases to around 22-23hg and that of course adds more timing.
I have mechanical timing set at 20 degrees, initial is at 14 and total is at 34, the advance rate with the springs that are in the distributor starts to come in around 1500 rpm and is all inn around 2700-2800.
I did have the mechanical advance set at 16 degrees with initial at 18 and total at 34 and that created a rough spot around 2400 rpm.
I’ve come to the conclusion that it likes a slower advance rate because when I increased mechanical advance from 16 to 20 which slowed the advance rate down from all in at 2400 to all in at 2800 the rough spot cleared up and got much better.
So for the moment I’m leaving mechanical at 20 degrees with initial at 14 and total at 34 all in by 2800 untill I have some time to play around with different springs to see if I can find an advance rate that is all inn by 3k rpm with 16 degrees of mechanical timing.
The problem is all the advance rate graphs I’ve seen there is nothing in between all inn by 2400 to 3500 with 16 degrees of mechanical advance.
And I’ve also come to the conclusion that the vacuum advance needs to be limited by a few degrees down to around 10-12 instead of 15.