1978 Johnson 4HP outboards Service Repair Manual P/N JM-7803, Page 76Get this manual
Quality of the image is intentionally reduced!
pressure to 16-18 psi (110-124 kPa)If pressure does not hold, submerge gearcase in water and check for source of leakageMake necessary repairs and repeat testScrew in vacuum testerPump out to 3"-5" of