This engine could have either a cdi magneto ignition or a points magneto ignition . The black wire coming out of the engine is the kill wire . It gets grounded to the engine to kill the engine , be sure it is not grounded when testing the ignition . If you have a point ignitiion it is possible that the points and condensor are the cause of no spark . If it is a cdi ignition the most likely cause of no spark is a failed coil or bad plug wire .
In either case it would be best to convert it to an electronic ignition . I would contact Bill Jennings at Bjs engine service or Adrian at CH ignitions for the conversion.
The 4.2 itself is literally indestructable and every bit as good as a G62 or any other 60 to 70cc engine . It is a heavier engine than the newer generation engines , but most warbirds need the nose weight anyway . I would run props such as Xoar 22x12 , 24 x10 or APC T6 racing prop to get that warbird speed .
anyway .