Hi
I have had similar problems over the past few years.
Some suggestions are:
1. Carburetor idle and main jets may need adjusting, especially if the carb has just been rebuilt.
2. Engine timing may be off.
3. If you are getting a good spark, check for oil and water condensation in the fuel tank.
4. Fuel pump problem

Remove spark plug, check spark, crank engine with coil wire removed so engine won't fire, and with a paper towel over spark plug opening. check paper for smell of fuel and signs of water.

Hopes this helps, good sailing.