first of all I took my merc 15hp 2 stroke and ran it all day long no plm at all. always cranks right up and runs so smooth. few hours later i tried to crank it up and it doesnt start after 100 pulls. checked the spark plugs, neutral switch has been by passed, kill switch is attached, full gas with open vent. still wont start at all no firing. whats the problem? then went home to pick up another motor a 2000 yamaha 9.9 2 stroke tiller and went back to the lake. cranks right up and idles great. the motor ran wide open no plm at all for 45 minutes. fished for few hours and then crank the motor up, starts right up and runs wide open throttle for 30 minutes all of sudden, the motor began to bog down and quit. wont START at all! checked everything and wont start. what is the problem with these 2 motors?