Yamaha power loss

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Orca2

Cadet
Joined
Jun 30, 2003
Messages
6
I use a Yamaha 50 DETO approx 1989 the motor starts and runs fine. After about 5 mins at maximum power the engine cuts down on revs to approx 2000rpm and will not increase. Selecting neutral will enable a higher engine speed but not when fwd is engaged. If I switch off and allow it to cool the engine perfoms normally again. There are no alarms sounding and there is plenty of oil in the tank. Engine does not seem over hot and plenty of water pressure at the pee hole. Thermostat seems to open ok in hot water and temp thermoswitch in the head operates at approx 95 deg.All plugs appear normal and identical. New water pump impeller recently fitted. Im stumped.
 
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MIKENVAHBEACH

Petty Officer 3rd Class
Joined
Apr 20, 2003
Messages
84
Re: Yamaha power loss

I have a 1989 225 yammy and had a similar problem. I had to replace the fuel lines and the fuel pumps, after that she ran like a top. You may also want to check the fuel filter to see if there is a blockage anywhere.
 
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Orca2

Cadet
Joined
Jun 30, 2003
Messages
6
Re: Yamaha power loss

Thanks Mike I'll try the filter but I feel this is an electronic problem rather than a fuel related one. This engine is in really good condition for its age and well looked after, flushed out of salt after every trip. Someone must have had a similar problem.
 
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spete

Petty Officer 2nd Class
Joined
Jan 27, 2003
Messages
168
Re: Yamaha power loss

My two cents ... could be a carb float sticking, crud floating around inside carb or perhaps the timing has gotten out of whack. If hoses are old they may be deteriorating and sending bits into the carb. <br />Would bet on the carb - maybe time for a rebuild. Easily done with a manual. <br />One thing I did when this happened to me was to let the fuel bulb go a bit soft/not pump it up extremely hard and it seemed to help (not sure but maybe this reduced the pressure inside the carb and kept the float from sticking)<br />I've also heard of fuel tank valves going bad and creating fuel supply problems.
 
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slufff

Cadet
Joined
Jul 5, 2003
Messages
6
Re: Yamaha power loss

I had same with a 70 and no one could figure it out. It turned out to be the electric primer was bad and allowed air into prime chambers,located in intake casting, and the motor had no power.Replaced center carb with primer located on it and it was like a new motor.
 
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