The only variables the ignition module controls, are spark timing and spark intensity. If you are getting a decent spark with a module you are testing but the engine does not run as well as with another module, the test module is giving you the wrong ignition timing. If the engine is capable of running backwards more or less steadily, the ignition timing is heavily retarded (probably firing at TDC or later, when running forward). There have been 2 stroke engines that were designed to be able to run backwards, usually to provide a cheap reverse for a motor vehicle. The system just retarded the ignition and cranked them backwards. An important issue is that when an engine rotates backwards the gudgeon pin offset is the reverse of what it should be, so wear patterns on pistons will be alarming and the engine won't last long. Way back when British car pistons used to have T-slots in the minor thrust face to permit closer fits and less piston slap, if you put them in backwards the piston broke very quickly, due to excessive side thrust on the T slot. The lesson is, don't run a 2 stroke backwards for any length of time unless you have changed the geometry to give you an offset between gudgeon pin and crankshaft axis that is in the right direction. Sometimes the offset is all in the piston, but other times the crankshaft is offset in the crankcase.
