Yamaha 115-225 HP Outboards Service Manual, Page 248Get this manual
ENGINE STALLSENGINE WILL NOT STOP
(B) Engine stalls when gear is changedIn addition to the above check points, go through the following:
Is something coiled around the propeller?
Remove it(P3-40)
Is the propeller stiff to turn in neutral?
Is the spark-plug tight?
Disassemble the lower unit and check(P6-16-4)
Tighten(P3-41)
Is the spark-plug gap correct?
Is the spark-plug in good condition?