Was the motor properly "winterized" before it was put into storage? Was a fuel stabilizer run through the motor and the boat's fuel tank. It sounds like your situation may be fuel related either from a delivery problem or possibly varnish or debris in an injector or the electric fuel pump. Check a sample of the fuel for being stale or water-laden.
A dealer will have to check out the fuel system on the motor and check pressures and flow to make sure the motor is operating as it should.
"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.
I agree with BluewaterBill.
Sounds fuel related to me as well. My guess would be a lack of fuel flow. Does the primer bulb get hard when you pump it up?