Since the op is running an aftermarket ignition, he needs a coil with the proper resistance for that system, not the factory system.
Does the paperwork that came with the system, or the company website state what resistance is needed?
Also, your problem may be elsewhere. Does the bike have a fuel filter that could be partially clogged up causing fuel starvation?
Is the fuel tank vent clogged?
Is the fuel line really old or really cheap? It could be delaminating inside, causing fuel starvation.
Have you recently done some work on the bike that might have kinked the fuel line?
New fuel filter and petcock, upgraded epoxy coated fuel tank, new fuel lines, clean carburetors, etc. But someone said it's better to rule out electrical problems first before anything else and I try to work that way.
The ignition system is a copy of Charlie's Place. Some basic assembly instructions and nothing else at all. I could write Charlie to ask him what coils he uses with his ignition, too (I didn't think so)