[Early_S_Man]

On centrifugal-advance-only Bosch distributors ... the point plate is fixed to the body of the distributor with 2 or 3 screws!

With fixed point plates, the only sources of dwell variation are:

1. Bushing wear causing radial play of central shaft

2. Uneven cam lobe wear on cam shaft -- #10 in diagram

3. Loose rubbing block on points

4. Worn or missing fiber washers or shims along central shaft causing excess end float (axial play) ... causing points' rubbing block to 'ride' up and down on the cam lobes

5. Bent central shaft

Or, some combination of the above ...

My suggestion is to remove, disassemble, and clean the distributor parts ... then reassemble dry and check for play in any of the above! Surely, something will be obvious with the amount of variation you are experiencing!

Be sure to lubricate central shaft with engine oil, and cam lobes with Bosch grease before reinstalling distributor in engine!