We are sorry to hear about the experiences you are having with the Evinrude E-TEC 115 HP. Your dealer should be able to take care of the issues that you described to us. If not, please contact email@example.com and include the dealer name and the engine serial number.
If what you call smoke is white or light gray colored, that is normal steam coming out of the exhaust relief due to the cooling water being sprayed into the hot exhaust section of the motor. You will see it in greater quantities when slowing down from being on plane. If the smoke is dark blue or black, then the engine has an internal problem and needs to be inspected.
Oil consumption varies with the load and rpm on the motor. More oil is used when the engine is accelerated quickly and initially when starting up. Fill the fuel tank to the top and the oil tank to the top and run the boat until the LOW OIL alarm comes on. Keep records of the fuel used and measure the oil needed to fill the tank, then do the math. Be sure your motor is propped correctly where it can turn between 5600 and 6000 rpm at full throttle with a normal load of passengers, fuel, and gear on board. If the rpm is less, you may be lugging the motor and requiring more oil consumption.
"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.