After your 30 seconds of running how long before you have another 30 seconds of running? Are you getting a good flow of gas at the carburetor inlet? It sure sound like poor fuel flow? I find as a rule with ignition problems it will run or not run. When you changed the ignition module did you check for any bad wires or poor connections? The only two other things are timing and compression witch it doesn't sound like. One other thing you can try is isolate the engine and chassis.