[5th_bike]

My first thought when i read this yesterday was, maybe some water got in the carb via the air hose between the filter and the carb, there could be a leak that lets in air, and water when it rains. Please check for snug fit and tighten if needed.
Another thought, water around the "kill switch" or ignition switch, in the handlebars. Or, water around the ignition coil, under the tank. Although I wouldn't know how it could cause the effects you describe - like a badly clogged carb...

Is there a way to test wires, yes, you need a multimeter. However there are a lot of wires and each has its function...
Download the manual, and look at the wiring diagram. Skip the wires to the lights and concentrate on those that have to do with ignition.