360 timing advance problems
I ran into the same issue on my D150 today. Replaced the pick up coil, set timing and when I reconnected the vacuum advance, bam. choked down. Ran across this discussion and didn't find any answers here so I thought I would add what I found.
When I replaced the pickup coil I didn't get the reluctor wheel correctly seated on the distributor shaft. The roll pin wasn't in the slot. So yeah, I could get it timed but it really wasn't in time. After getting the reluctor properly seated on the distributor shaft, and re-adjusting the timing, the vacuum advance works like it should now.
So if you have been into the distributor or had it rebuilt, check to make shure the reluctor is seated properly and make sure the roll pin is in the correct slot on the wheel. The slot between the slashes is for small blocks, the other is for big blocks.