I am facing somewhat similar issues with my '94 GTS and am pretty sure my problem is my MPEM. Some of the potential causes of no spark that I have mined from the forum so far are as follows:
It is possible for there to be corrosion on the coil ground connection which can cause intermittent or permanent loss of spark. Likewise, a bad MPEM could be causing spark failure (see below). Some machines have a connector between the stator and the electrical box which can corrode over time and prevent the energy from getting from the pickup coil to the ignition coil but I do not believe the '94s have the plug unless someone has added a connector to yours. Also, aged spark plug leads could cause a loss of spark. Many people unscrew the plug caps and trim back a few millimeters of lead to eliminate corrosion. It is likewise possible to trim the coil end of the spark plug leads.
The following is what I have deduced troubleshooting my loss of spark and may not be 100% . The ignition electrical energy and pulse rate (based on RPM) is generated by a magnet on the fly wheel turning past the pickup coil (stator) under the flywheel. The electricity flows into the electrical box and to the positive side of the ignition coil which uses the RPM frequency to generate the high voltage for the spark plugs timed to fire appropriately. The wire that attaches to the positive lead of the coil has a tap that connects the coil to the MPEM. The MPEM has internal circuitry which essentially shunts the the electrical signal intended to go from the stator to the coil to ground either as a rev limiter function or if either the lanyard is pulled off or the kill switch is depressed. This is why a shorted MPEM can cause a loss of spark.
To test your MPEM, it is possible to pull the electrical box, open it, hook everything up as it would be normally and try starting the machine. If you have no spark, try unplugging the lead that runs from the positive lead of the coil to the MPEM and re-try starting the engine. Be aware that all safety features run through the MPEM so if the machine starts, you have no way of stopping the engine without either unplugging the positive lead to the coil or plugging the MPEM back in. Be very careful doing either as there is going to be high voltage floating around in the electrical box with the engine running and high voltage electricity can hurt/kill you. If your engine runs with the coil to MPEM lead unplugged but not when it is plugged in, then you MPEM is toast.
I hope my ramblings are helpful. If I am way off in my understanding of how the ignition system functions on these old two strokes, someone more knowledgeable please correct me.
Doug
