D 400 engine

The D-400 series engine or the Iron Horse engine was a light-duty two-stroke engine used for powering lawnmowers produced in the 1960s to the early 1980s. D-400 engines were single-cylinder engines designed and manufactured by the Outboard Marine Corporation (OMC; Johnson and Evinrude) for Lawn-Boy and Masport. The D-400 engines displaced 109 cc, generated 2.61 kW of power, and operated in the range of 2400-3300 RPM. The engines have a distinctive rectangular cowling that has created a nickname of Brick-top mowers. Another distinctive feature is the two-finger vertical recoil starter. The kidney-shaped muffler and exhaust unit is mounted beneath the mowers' deck and gives the engine a small, low profile design when compared to the newer and more powerful lawnmower engines. The ignition system employs a magneto, points, and a condenser (capacitor) set-up with an unusual spark-advance system which utilised a weight on the crankshaft to adjust the spark-advance amount depending on engine speed. The sprung governor was also unusual with a throw-yoke which operated under the flywheel and was linked to the throttle. The carburettor was a float design and fed into a pair of reed valves.

The D-400 engines are now a popular engine restoration job due to their distinctive shape and low cost. Parts, however can be difficult to source and therefore multiple engines are often bought to satisfy part requirements. The recommended oil:fuel mix is either 16:1 or 32:1 depending on age. In New Zealand and Australia, Masport offered the D-400 engine on their Premier, Premier II, Rancher, Rotacut, and Tornado models. In this Oceania market, the D-400 was called the Iron Horse engine.