Rotor play, uneven timing, question

I have a 1972 dodge dart with a 360 and just bought a rebuilt distributor (points type) from the auto parts store and installed it with a pertronix ignitor kit. The timing jumps around a lot. I pulled the cap off to see if there was something wrong there, and I noticed that I can turn the rotor left and right about 10-15 degrees with great ease, (and it stays there, like there is no spring pulling it back into position). I pulled the distributor and the oil pump drive shaft/gear assembly to see if it was worn, it was not and it fits snugly in the slot. Could it be that the centrifugal advance springs are weak or not even installed? Thanks for any help.
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