Initial dissection, Bosch roller cell Pump. Pump Strainer, internal filter, on the left.

Further disassembly, armature rides on shaft fixed to baseplate of pump cell. Bushings were good, brushes ok.

Closeup of pump cell parts, all seemed in good condition.

Armature is connected to rotor with this nylon adaptor.

Adaptor teeth slip into these small slots in the rotor.

Closeup of commutator segments, Worn down but still clean.

Here is the problem, the internal pump filter is almost totally plugged, the small area I cleaned shows what it should look like, this results in pump cell cavitation, and accounts for the fluctuating rpm, the pump cell receives very little fuel, and results in low to mid draw, low to high rpm.

Here is a better image of the internal filter with more of the crud washed away, its a wonder anything passed through it at all. The pump itself probably would have lasted longer if not for the plugged filter. The noise from the pump has to be the cavitating pump cell.