The Eisemann GV was begat after the famous G.. series, like the G4. It was not as massive and robust but was not plagued by the usual potmetal issues. It was standard equipment on many gas powered Caterpillars as well as some Allis Chalmers and Kohler light plants. Some 2 cylinder versions were used on gas pony motors on early diesel tractors. They were actually an excellent mag with proper care, smaller, but hot. Beware of insulation seepage. They like any wound armature are very subject to sticky goo. Their brass armature endcaps have the steel driveshaft molded in and are more fragile than the larger G series. If it gets gooey, it is time to rewind. Here are some tips to help keep yours well. The manual specifies a plug gap of 1/32" and of course non resistor plugs and solid wires. The points should be set at about .012-.014" or .3-.35MM. The nut and adjusting screw as well as the screw that holds the points in are metric sizes.
The GV and GS series used a lot of 4mmx.75mm threads (Not the standard metric 4MMx.7) inside for their safety gap screw, timing pointer,armature end caps and 10-32 threads on the outside. There are also metric threads lurking in some of the later Eisemann magnetos as well.
These images are from the Eisemann Caterpillar application service manual.
Note how plug wires are to be connected. Mr Eisemann did not make it easy.
There were some later versions fo the GV4 that had taller distributor posts and would accept the common plug in wire ends.
Always be sure that the mag impulse coupler does not crowd against the float and the tractor drive hub as described above. This will stress the impulse coupler and may cause the impulse to not engage and retard the spark when starting causing an armbreaker.
Your mag is probably out of warranty.
Sticky goo from deteriorated insulation varnish.
This is one that suffered from sticky goo from deteriorated armature insulation and got a mighty crank. The shuttle pole shoes were glued to the stationary poleshoes and the steel driveshaft turned in the brass endcap and dug into the condenser.