1988 Johnson Evinrude "CC" 9.9 thru 30 Service Manual, P/N 507660, Page 86Get this manual
8Point end of fuel hose into container below top of tankDepress the ball in the fuel connector until any remaining fuel is expelled9Add air to bring pressure back to 10 psi (69 kPa)f51 10Close air release valve on adapter and remove Stevens E.J pressure tester 11 Submerge fuel tank in water, one portion at time, in the same manner you would check tire for air leaksAny air bubbles indicate leak point which must be repaired or replaced