I had a similar problem on a 1954 PU.

Some one had put a 216 distributor it the truck with 235 cap and rotor.

The 216 shaft does not stick up enough to lock in the 235 rotor key well so the rotor would slip out of time.

In this case it always started as the rotor droped back in the key when cranking with the starter but jumped out on the road.


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