[1crosscut]

Are you sure that it is actually overheating?
Use a meat thermometer placed directly in the coolant to measure the temperature. Knowing the temperature for sure will help with any diagnosis.
You should not have steam coming out of the cap. Any water or steam should only come out of the overflow tube. Probably a bad radiator cap gasket causing that.
Are you adding coolant on a regular basis? If so perhaps you have the radiator filled too full and it is pushing the excess out. Don't ad any as long as the tubes are covered you are good to go.
Timing set correctly? Retarded spark will contribute to overheating.