The centrifugal advance mechanism under the rotor has a habit of rusting. I dismantle everything, (pull the drive gear, and the shaft, too) and buff it all clean with a power brush on the bench grinder. Some advance weights have bushings, others don't. All are bad about wearing the pivot holes oblong and getting uncertain on the advance. I make new bushings in the lathe, and reassemble everything with a little white Lubriplate grease. Spin it up on the distributor tester, set the advance curve the way you want it by adjusting spring tension and the length of the pivot slots, and you're good to go.
If you don't have all the equipment to do that, find an oldtime race mechanic who does. IM me for more details if you like.
Jerry
