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1989 200HP 2-stroke RPM Rollback

PITA

New member
Help, 1989 Yamaha 200HP Outboard 2-stroke carb engine theRPMs rollback intermittently. The engineidles and runs great for 30+ minutes before having an issue so I need sometroubleshooting/repair advice.
I’ll run 30-45 mins at high cruise RPMs in the 4000-4300range then suddenly the engine will rollback to 3000 RPMs with no throttle ortrim changes. Occasionally it surges and/orslows to 2000 RPM happen as I continue to run home &/or cycle the throttle,that’s the max RPM I can get. The engineappears to enter into a safe mode but I have no alarms for over temp or low oil. If I shut the engine off for a while, she’llstart & cruise again for short distances. Once the problem starts, it's stalled occasionally but usually it keeps running just at thatreduced RPM.

I’ve checked & replaced the fuel filter and the water separatorplus I inspected the vent screen and verified the clean line. I only run ethanol free gas & addstabilizer with each fueling. I replacedthe primer ball and have checked all the fuel lines with no leaks or bad linesobserved. The spark plugs were new thisseason & all look good upon inspection. The console & engine linkages look good on both ends. Thewater pump seems fine and produces a solid stream but I’ve inspected the 2 x temperaturesensors (which are intact and look good) along with the thermostat. I top off the oil system before each trip butconsumption & reservoir appear normal/remain full on each trip.
Again, no alarms or additional engine lights beyond thegreen oil system.
Anyone fixed a problem like this? Thank you

 
I have seen this before, If all alarm systems and the guardian system is working........

I would pull the carbs and look for some debris around the inlet side of the float needle seat.

Take each needle valve and rotate it in the seat and make sure it does not bind. When this has happened in the past I have found debris on the inlet side of the needle seat. I have also found the needle it self bind in the seat if rotated in the correct position causing an intermittent loss of power as you described.
 
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