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my 1990 150 yamaha is now suddenly dead on the bottom 2 cylinders. it all started when all of a sudden it was lacking power and had couldnt make WOT rpms anymore like i had 1 or more dead cylinders. with the throttle wide open i could occasionally feel them "kick in" for a split second and get full power but it was generally gutless.
got home and began troubleshooting. i have spark on all 6 cylinders and compression is a dead even 135 all around. and all the plugs were nice and tan. BUT as it idled i started pulling plug wires and it became apparent that the bottom cylinder in each bank was not firing because when i pulled those plugs the motor didnt react. i notice that these are fed off the same carb.
fuel is being pumped to all the carbs though and i pulled the main jets and found them to be clear of debris. however when i remove the silencer and run the motor it feels like there is little or no suction (vacuum) on the bottom carb whereas i can feel it sucking pretty hard when i put my hand over the other 2.
i wonder if theres a major vacuum leak? or could reed valves cause this? i ordered a carb rebuild kit but it seems wierd that it would completely shut down when it had been running perfect all day. Any thoughts?
got home and began troubleshooting. i have spark on all 6 cylinders and compression is a dead even 135 all around. and all the plugs were nice and tan. BUT as it idled i started pulling plug wires and it became apparent that the bottom cylinder in each bank was not firing because when i pulled those plugs the motor didnt react. i notice that these are fed off the same carb.
fuel is being pumped to all the carbs though and i pulled the main jets and found them to be clear of debris. however when i remove the silencer and run the motor it feels like there is little or no suction (vacuum) on the bottom carb whereas i can feel it sucking pretty hard when i put my hand over the other 2.
i wonder if theres a major vacuum leak? or could reed valves cause this? i ordered a carb rebuild kit but it seems wierd that it would completely shut down when it had been running perfect all day. Any thoughts?
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