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Discussion Starter · #1 ·
02' 50 horse 2-stroke Yamaha been running fine till this morning. was on plane around 4400 rpm when the engine lost power making a noise like a cylinder was miss firing or not getting fuel. checked fuel filters they were clean (brand new 10 gallons in a 10 gallon tank). Also i was getting an alarm but dont know what for, the engine was peeing fine and had oil in the reservoir. I was able to limp back at 2000 rpm. what was interesting was at this rpm if i trimmed the motor down the alarm went off, when i trimmed up it would quit. Thinking it had something to do with the oil??

I have had the engine for 2 years and have not done any carburetor work. I put fuel treatment in the tank regularly. I assume the carb is gummed up and hope thats all it is. Any suggestions or thoughts about what could be the problem thanks in advance!
 

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a fuel problem will not make the alarm sound or put it in to rpm reduction mode. which is about 2000 rpm, even though the the water pump is peeing fine you could have a stuck pressure control valve ( poppet valve) causing it to over heat at a higher rpm causing the alarm and rpm loss. when is the last time you serviced the poppet valve,? this is where i would start..
 

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Kinda sounds like the water pump may not be operating to full capacity and turbulence, when trimmed all the way down, is causing water volume loss. Plus, this cooling system relies on the thermostat to control all the cooling flow. If the thermostat is partially blocked or not working correctly, you can have temp issues when trimmed down due to "loading" of the engine causing higher internal temps. Easiest to check.... thermostat. If your water pump hasn't been changed in two years, I would recommend that anyway. I have had the oil level sensor malfunction before from vibrations causing the float to sink or some moisture to make contact across the terminals, but it is rare. First thought is overheat.
 

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Discussion Starter · #4 ·
found that the water pump was not functioning at capacity, changed it out and the thermostat. engine is running fine now. thanks for suggestions
 
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