Do you have a multimeter? If not get one because they are good for pinpointing electrical problems like discharged battery, bad connections, faulty ignition switches and starter solonoids. I think you've probably got two seperate problems - an electrical problem with the starter motor circuit and something else which is stopping the engine from starting when the starter motor does work. Take a spark plug out and connect it up to the ht lead, then earth the plug against a metal part of the engine. Turn the engine over and check that there is a good spark. If the spark is good pull the fuel inlet pipe off the carb and turn the engine over - fuel should come out. Watch you dont set it alight though! If that's O.K. it's probably a carb problem.

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