I bought this WNP-200 welder/generator by Chemtron, a.k.a "the bug" at an auction for a pittance, and have been working on it, and have some questions.

I can't get a spark, and checked the negative going to the battery, and it is connected to an isolated ground, it seems. the bolt connecting to the chassis has Bakelite washers to insulate it (?). My question is this, how can I get a spark, if the juice going to the spark plug electrode cannot complete the circuit to the engine casing and back to the battery negative terminal?
Is anyone familiar with this kind of setup, or does anyone have a schematic/wiring diagram that might shine some light on this?, perhaps even a manual? any help would be appreciated.
The onan motor has a fuel pump that is not pumping, but I feel it pumping air, so the pump is probably ok, might be something like a hole in the suction line, not enough gas in the tank.