Have you established for sure that this is an ignition problem? You can do this quick and easy with a cheap neon timing light from the bargain table at the local autoparts store. Just mount it someplace where you can watch it safely, hook it up and go for a ride. If it stops flashing when the bike craps out, you know to dig into the ignition. If it still flashes, look for a fuel problem. This is beginning to sound like the 'secret' fuel filter in the T fitting at the carburettor end of the fuel line might be partly blocked.
