1978 Johnson 4HP outboards Service Manual, Page 10Get this manual
SPECIFICATIONS Models 4W78 Weedless gearcase, standard length 4R78 Standard gearcase, standard length 4RL78 Standard gearcase, long shaft
LOWER UNIT
Cool ing system Combination positive displacement and centrifugal pump17:28 Weedless 12:25 Standard Part Number 316558
Propeller gear ratio Propeller drive pin
POWERHEAD
Horsepower (S.I.A- certified) hp at 4500 rpm 4000 to 5000 rpm
Propeller
Standard7-12" dia 6" pitch, brade pi astic Weedless6-14" dia 6" pitch, blades plastic
Full throttl e
operating range Test tonk rpm with test wheel
Propeller 3800 rpm Part No316021 for Weedless 4550 rpm Part No317738 for Standard
MISCELLANEOUS
Speed control Single lever, synchronized throttl and spark Weedless38.0 Ibs(17.2 kg) Standard38.0 Ibs(17.2 kg) Automatic rewindnylon rope
Idle rpm Engine type
700 rpm 2-cylinder, cycle alternate firing 1-916" (39.69 mm) bore 1-38" (34.93 mm) stroke 5.28 cubic inches (87 cm )
Bore and stroke