... to go along with what JW51 said, the mechanical advance starts kicking in at about 400 RPM in these distributors, so make sure the engine is idling at or below that speed before trying to set timing to the BB. I like to set mine on the BB with a timing light and then use the "RA" adjustment to advance the timing a little bit to find the sweet spot. The advantage in doing it that way is you can always get the adjustment back to stock without a timing light.
'57 GMC 102, Original 347 V8, HydraMatic, 3.08 rear gear, added A/C, disk front brakes, HEI, AFB carb, '98 Honda Black Currant paint. T-boned and totaled 10/12
'52 GMC 152 Stake Bed, Original 228, SM420, added A/C, HEI, disk front brakes, '67 Chev 3.55 rear gear. Gets used as a real truck.
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