It could be a faulty voltage regulator has cooked your battery. Try checking the battery with a proper load tester. If it is flat, charge it up and re-test. If it is then OK see what the voltage is with the engine running at various RPM. Any more than 15v and you need a new regulator. If the starter doesn't work with a good battery, put a test lamp between starter motor live lead and earth, press the start button, if the solenoid clicks but the lamp doesn't light, you have a faulty solenoid, if the light comes on but the starter doesn't spin, you have a faulty starter, it probably just needs new brushes.

 

I thought I'd add a question to the thread. My carburetor doesn't have an air/fuel mixture screw on it, just a blank (see picture). Any thoughts? I am also having a sputtering at initial throttle problem. Only happens in High gear, not in Low.

 

I'm having the same problem and just rebuilt the carb with new ports and replaced the spark plug. It only happens in High, not Low. I tried to locate the fuel air mix screw but only found a blank (see picture). Anyone come across this?