That's a very common problem with all makes of smaller 4-stroke carbureted outboards, especially after storage or being sitting unused for a while. The tiny passageways and jets inside the carb are plugged or restricted with dried fuel deposits or possibly debris.
A thorough carb cleaning, preferably with an untrasonic cleaner, and a repair kit normally takes care of the problem. It is recommended also to flush out the engine's fuel system and to use fresh gasoline with a fuel stabilizer added such as Evinrude 2+44 Fuel Conditioner.
"There is never just one thing wrong with a boat";
-- Travis McGee, main character in a book series by John D. McDonald
The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.
The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.