Yamaha 115-225 HP Outboards Service Manual, Page 243Get this manual
THRTBGLENGINE WILL NOT START IS -NO Is the spark-plug installed correctly?
-,Install it correctly(P3-41)
Does the piston face correct direction? YES
Correct(P5-18)
Remove the cylinder-head and check, is the piston holed?
Replace(P5-10)
Is the head gasket in good condition?
Replace(P5-10)
Is the piston or cylinder cracked, scratched or deformed?
Replace(P5-12)
YES Is the piston ring damaged or worn?
Replace(P5-13)
Are the seal-ring in good condition? {}YES RE-CHECK