40 hp 2 stroke 1989 model Yamaha outboard stalling

Joined
Jun 14, 2017
Messages
2
Recently my motor started losing power going across the lake. The throttle would be full on but the motor would slow to roughly half throttle without moving the position of the lever. It never cuts out or sputters at all though. Then, randomly it would speed back up and run normal. It would go back and forth up and down all the way to the dock.
 

99yam40

Fleet Admiral
Joined
Sep 7, 2008
Messages
8,851
a cylinder cutting out due to too little or too much fuel or loosing spark could cause this.
check the fuel pump for leaks fouling #3

check spark and timing if fuel pump is OK
 

ClassicAQ

Petty Officer 3rd Class
Joined
Jun 2, 2017
Messages
78
Sounds fuel related to me. Dump the fuel from each carb bowl into a white cloth. Look for debris. If you discover some, this is what's stuck in your carb jets. Otherwise, when was the last time you pulled the carbs for cleaning? The symptoms you've described is what would occur with clogged high speed jets in one or all of your carbs.
 
Joined
Jun 14, 2017
Messages
2
I didn't find any debris in any of the bowls at all. I changed the in line filter also, but it looked like new. I was wondering if it could possibly be anything electrical? I didn't know if there was anything electronic in the throttle control system that could malfunction. In my experience with mechanics on vehicles (I don't know jack about boat motors!) when there is a fuel flow problem there should be some hesitation in throttle response or some sputtering at some point from being fuel deprived? Outboards seem to be the most illogical irrational bass ackwards kinda mechanical contraption I have ever touched though so I'm confused! Thanks!
 
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