493 carburetor tuning question

Mattax said
Interesting. That's pretty sensitive (1/2 turn of the screw). I'll check a 4779 double pumper next time I'm at the garage.

I was pretty tired last night. Once I started looking at your notes I completely agree there is an issue with the distributor.
View attachment 1715726265

On an MSD, use springs in pairs so the tension on both weights is the same.
Timing will advance in a fairly straight line.
There should be enough initial tension so the initial timing stays pretty much the same up to the actual idle rpm.
If the engine is idling at 950 rpm, then when its put into gear (assuming automatic transmission) the goal is the least drop in rpms. But if it does drop a little, and it probably will, its important the timing stays the same. Otherwise manifold vacuum will go down with the reduction in timing. With less vacuum, less fuel pulled through the idle systemswhen if anything it needs a little richer when placed in gear.

Something like the solid green line would be reasonable.
And then when experimenting with a little less initial, the whole advance shifts down as illustrated by the dashed line.
View attachment 1715726279

Leave the vacuum advance disconnected for now, but one of the reasons for using a slow rate of advance is planning for the vacuum advance to be used.

So I pulled the distributor today and I couldn't find anything wrong with the springs or weights. They have no slack, consistent tension between the two and they move smoothly. Just for the sake of it I lubricated them with some white lithium. Put it back together and started the car. After warming up I set up a timing light and without touching anything I could watch the timing move anywehre from 20 degrees to 32 degrees. So I pulled it again and looked more closely and there were some markings on the shaft on the distributor where it goes into the drive gear. (See photos) they are on opposite sides as if it was slapping in the slot of the drive gear. So I pulled the gear and took some measurements. With the gear fully engaged 3/8ths or .375 inches of the distributor shaft engage with the gear. I took measurements and being generous I found the MOST the gear is engaging is actually .226 inches. Which causes some some play in the mechanism and most likely caused the marking in the picture. I think this explains my inconsistent mechanical advance. My question is do I get a different gear or do I need to bite the bullet and get a different distributor. Obviously if I get a gear with a longer shaft it may not engage on the cam as much since it will be sitting .149 inches higher supposedly...