The Johnson 50-horsepower outboard motor was produced by OMIC in five model years, 1990 and 1991, followed by 1999, 2000 and 2001. There were some significant differences between the models, even though they shared some systems. One of the greatest differences was that one motor was a 2-cylinder 2-stroke motor, while the other was a 4-stroke 3-cylinder.
Two- or 4-Cylinder, 2- or 4-Stroke
The Johnson 50 came in two configurations. One, with a 2-cylinder, 2-stroke powerhead and one with a 3-cylinder, 4-stroke powerhead. The 2-stroke version was produced in 1990 and 1991. The motor reappeared in 1998 as a 4-stroke engine, and production continued until OMC, Johnson's parent company, went into bankruptcy while producing the 2001 model-year outboards. When Bombardier Recreational Products acquired OMC, Evinrude and Johnson in 2001, Bombardier dropped the 50-horsepower motor from its productions schedule.
The 50-horsepower 2-stroke motor build between 1990 and 1991 had a cylinder bore of 3.19 inches and a piston stroke of 2.82 inches. Because the motor had a 2-cylinder powerhead, the total displacement of the motor was 45 cubic inches. This is somewhat different from the 4-stroke motor produced for the 1999, 2000, and 2001 model years. The later motor had a cylinder bore of 2.80 inches and a stroke of 2.7 inches. With a 3-cylinder powerhead, the total displacement of the later motive was 49.7 cubic inches.
Ignition and Electrical System
The the 1990 and 1991 model had two different starting systems. These included a recoil starter -- a pull-rope -- and a tiller-mounted electric starter. Motors equipped with the recoil starter came equipped with two options for priming the fuel pump prior to an attempt to start the motor. One, a primer bulb, was manually pumped to prime the fuel pump. The other option was an electric fuel pump primer. The 1999, 2000, and 2001 models were equipped with remote electric start. The electrical system is a fully transistorized battery powered system controlled by the motor's electronic control unit.
Lubrication and Cooling Systems
The cooling system for all models of the motor was a raw-water cooling system. Openings on both sides of the motor's lower unit admitted water from the body of water in which the motor is operating. The water was distributed throughout the motor by an impeller-type water pump located on top of the gear case. The pump was thermostatically controlled. The lubrication system options for the 1990 and 1991 models of the motor included the OMC AccuMix system, with 2 fuel pumps and an engine-mounted oil mixing chamber. These models also offered the variable ratio oil mixing system, a lubrication system that mixed oil with the motor's fuel. The motors produced for the 1999 through 2001 model years, all 4-stroke motors, were equipped with a crankcase, requiring regular oil changes every 100 hours, according to the motor's maintenance schedule.
- "Evinrude Repair Manual -- 2.5 to 250 HP Models, 2002-2007"; Seloc Marine; 2007