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HOTRODSRJ,
I want to thank you for spiking my curiosity about the different vacuum advance units available. I just got a different Distributor from a friend and decided to try it out in my 262"SBC truck engine. I was shocked when I plugged in the vacuum advance and the initial timing jumped from a set 12º to 38º!
So I took it back out and removed the vacuum unit and compared it with two uther units I had on hand.
What I found was the amount of travel available for the actuator rods to move before they hit the end of the "slot" in the housing varied by .100"!
That's a lot of degrees of advance!
the three units are stamped "B1", "MS 421-24", and B25.
The "MS" one was the high potential degree pull one, being able to move around .278" while the "B1" can only move .198" and the "B25" moved only .190". That's the one I used. I'm happy with that.
I also raised the secondary rods so they will start and come in richer by using a "H" hanger which is .010" higher than the "K" that was in the carb. Actually I bent one of the "universal hangers" to that dimension. didn't stumble at mid range on a trip around the block. I'm going on a 100 mile round trip tomorrow so I'll see if everything's hunky dory now.
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