I thought you said a long time back that you had replaced the points and cond. A bad cond will do exactly what has happened to you. However, I expect that Hotrod is right, you have the timing 180 degrees out. However, I have done this and at least got some kickbacks out of the engine.
You said you had a backfire through the carb which makes me think even more that you are 180 out.
Starter fluid will make an engine fire even if there is no carb on the engine. All it takes is spark at the right time and the starting fluid since it is already atomized which is what a carb does! Of course it won't run but a few turns, but it will start and tell you that you have spark and that your timing is probably ok.
Anytime an engine backfires it is either out of time or too lean.
