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Old 22-01-2010, 21:56   #31
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When you replaced the fuel line, did you replace the bulb? When you pump the bulb in the fuel line, does it pump up to a firm bulb. I had a bulb with a minor air leak in it and it drove me crazy til we found it. Same symptoms; idle great but no power on full throttle. Even new bulbs can have this problem.
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Old 22-01-2010, 22:25   #32
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When you replaced the fuel line, did you replace the bulb? When you pump the bulb in the fuel line, does it pump up to a firm bulb. I had a bulb with a minor air leak in it and it drove me crazy til we found it. Same symptoms; idle great but no power on full throttle. Even new bulbs can have this problem.
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Old 08-05-2012, 16:23   #33
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Re: Yamaha Outboard - No Power

I know this is an old thread, but I too have been having these same problems with my port motor, just checked and it also was put back together the wrong way, I have pulled it off and cleaned it a dozen or so times each time putting it back on the same wrong way, then I read your post and checked it and compared it to the other motor and bingo, if only I had read this post earlier, thanks for the help!
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Old 08-05-2012, 19:02   #34
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Re: Yamaha Outboard - No Power

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My 9.9 Yamaha had a multiple trip to the mechanic's until we found the problem. There is a low oil pressure sensor that will cut it back to idle if it thinks the oil pressure is low. We found the sensor and cut the wires. Runs like a bad dog now. He also took out the thermostat. It was plugged and he thought it might be causing it to get warm and idling down on high heat. All is good now.
I tried everything, even exchanged every part possible with my starboard motor. Checked all my wires then found the oil ligt broken, checked the oil and it was really low, topped it up and it now runs, will keep an eye on it to see if there is a leak.
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Old 09-05-2012, 07:00   #35
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Re: Yamaha Outboard - No Power

Greetings and welcome aboard the CF, HueyHuey.
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Old 13-05-2013, 15:45   #36
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Re: Yamaha Outboard - No Power

I have a Yamaha 9.9 4 Stroke.I am having a similar problem, except when I put it into reverse it appears to have a lot more power and the engine seems to rev up to higher RPM's.
Any thoughts??
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Old 08-09-2014, 20:34   #37
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Re: Yamaha Outboard - No Power

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Originally Posted by Jmolan View Post
My 9.9 Yamaha had a multiple trip to the mechanic's until we found the problem. There is a low oil pressure sensor that will cut it back to idle if it thinks the oil pressure is low. We found the sensor and cut the wires. Runs like a bad dog now. He also took out the thermostat. It was plugged and he thought it might be causing it to get warm and idling down on high heat. All is good now.
Good night sir
I contact to ask me more about the solution he found to his problem
I have a 9.9 HP fourt stroke yamaha 1994 model and this works fine, lit perfect and excellent low or minimal work, but if your speed or rpm is increased, overheats
my mechanic shows a lack of pressure in the oil (almost no pressure in psi) and believes that this is not due or the oil filter or oil pump, maybe a problem with the cdi, but can not find solution
I would be very grateful to you or anyone who can help me find the solution to my engine, excuse my bad English
Mauricio
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Old 09-09-2014, 05:21   #38
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Re: Yamaha Outboard - No Power

Greetings and welcome aboard the CF, Steamfitter, and Mauricio.
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Old 10-09-2014, 19:18   #39
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Re: Yamaha Outboard - No Power

Mauricio,

I am sorry to hear about your problems, hopefully I can help you. Additionally, your English is much better than any foreign language I speak!

To begin with, low oil pressure usually does not cause overheating. Low oil can, because oil also carries away heat but oil pressure by itself does not.

How do you know it overheats, does it start smoking or sizzling?

Will it run at full power before it overheats and then the power starts decreasing?


If it has not been done yet, the thermostat needs to be removed and tested. It is located on the top of the engine between the drive belt pulleys. Remove it and put it in a pot with water and put on the stove and have a thermometer. Look at the thermostat, it is closed but should open up when the water reaches 60C. If it does not, replace it.

The water pump impeller also needs to be inspected, you will need to pull the "lower unit" off to do that. It is simple but much easier if you have someone show you the first time. If the impeller is worn or broken, replace it. clean the passages out with wire or blow them out with compressed air.

Reassemble those parts and then adjust the carburetor, as running with too little fuel (called "lean") can make it run hot too. First adjust the idle by connecting a tachometer and adjusting to 950 RPM, +/- 50 RPM, then adjust the linkage.

I hope that is a help!

Regards,

Mark
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Old 04-04-2017, 12:21   #40
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Re: Yamaha Outboard - No Power

Hi, I have a Yamaha 9.9, 4 stroke outboard 1984 year of manufacture, before winter it was fine although it was getting difficult to start sometimes...it seemed as if it was losing fuel. now that i'm up and at it..it would not start..I've had the carb off and cleaned it..(yes it is reassembled correctly)..I've had the fuel lines off and checked them and they seem.
Like you I can get it started now but as soon as I put any load on it I get the same symptoms as you did..I've had the plugs out and checked them and they seem fine although i'm not sure what the gap should be...but they aren't choked up or all oily, the oil was low and so I topped it up...any ideas

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Old 04-04-2017, 12:44   #41
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Re: Yamaha Outboard - No Power

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Originally Posted by rogueisland View Post
Hi, I have a Yamaha 9.9, 4 stroke outboard 1984 year of manufacture, before winter it was fine although it was getting difficult to start sometimes...it seemed as if it was losing fuel. now that i'm up and at it..it would not start..I've had the carb off and cleaned it..(yes it is reassembled correctly)..I've had the fuel lines off and checked them and they seem.
Like you I can get it started now but as soon as I put any load on it I get the same symptoms as you did..I've had the plugs out and checked them and they seem fine although i'm not sure what the gap should be...but they aren't choked up or all oily, the oil was low and so I topped it up...any ideas

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Rogueisland

Did you leave fuel in it all winter?

What I found on mine with the same symptoms is the fuel metering jet in the carburetor was full of corrosion. Modern gas today has alcohol, which retains water. So if you let it set for long periods the moisture in the fuel will start to corrode its aluminum carb, which in turn plugs up the jet. You can unscrew the jet and run a wire thru it or replace it. I use to carry an extra jet.

Other then that I'd say test the compression.
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Old 04-04-2017, 12:53   #42
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Re: Yamaha Outboard - No Power

Thanks for the suggestion, i'll get the carb off tomorrow

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