Base Timing Problem

[sleepydsm]

When I tried to set my base timing awhile back I had a problem. The timing mark was jumping all over the place. I have set the base timing before on these cars many times, and it normally sits still in one spot. My problem is the timing mark moves very erratically.

*Grounded with a jumper wire to the battery
*Timing light hooked to #1 plug wire

Any one have ideas? Bad CAS?