Carburator needs cleaning&ajust. Put som BG in the tank. Inspect ignition system for component wear. Compression cud b weak. Buy a clymer or haynes repairbook
With this much info, its going to be hard to diagnose... Replace all 3 spark plugs with the correct "surface gap" ones. Make sure the battery is FULLY charged! Check the rotor button and the cap for signs of shorting..(dark streaks or smudges inside the cap). The rotor button and the cap condition are CRITICAL!