1991 Yamaha Outboard Factory Service Manual 9.9 and 15 HP, Page 61Get this manual
Crankshaft 1Check the connecting rod axial play at the small end to determine the amount of wear of the crank pin and the bearing at the big endIf small end play exceeds tolerance, disassemble the crankshaft and check the connecting rod, crank pin, and big end bearingReplace defective partsPlay after reassembly should be within specificationRod axial play: mm (0.08 in)
Reed valve assembly Inspection
1I nspect the reed petals for signs of
fatigue cracksThe teed petals should fit flush or nearly flush against the neoprene seatsIf in doul)t as to sealing ability, apply suction to the carburetor side of the assemblyshould be slight to moderate2Check valve stopper clearanceIf beyond tolerance, adjust the stopper or replace as requiredValve stopper clearance: 9.9N1.3 mm (0.05 in), 15N: mm (0.16 in) If clearance is 0.1 mm (0.004 in) more or less than specified, replace the valve stopper
2Check the connecting rod side clearance
at the big endIf clearance exceeds tolerance, disassemble the crankshaft and replace any worn partsBig end clearance should be within specificationRod side clearance Minimum 0.20 mm (0.008 in) Maximum 0.70 mm (0.028 in)