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Old 13-12-2009, 10:04   #1
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Yamaha Outboard - No Power

Pulling my hair out over this one.... Yamaha 15hp 4-stroke outboard (F15ESHY model) starts and idles fine, but will NOT respond to wide open throttle and will not get the dink up on plane. When I goose it, the engine sounds like it's bogged down.... low growl. I can put along just fine, with the engine a few hundred RPM above idle, but it makes no power and can't begin to get the dink on plane. (11ft Achilles RIB)

I've had it to the shop (without success) and after many $$ here's what has been done so far:
- new ignition coils
- new flywheel sensor
- new carburetor
- repaired the engine fuel pump (rubber diaphragm had been leaking)
- new plugs
- "tune up" whatever that means..
- new fuel hose
- new fuel tank

The outboard shop said they were stymied.... well DUH it's not fixed.

Before I go throw $90 / hr at another incompetent shop, is there something I should check?
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Old 13-12-2009, 10:18   #2
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It sounds like fuel starvation. You said you replaced the fuel hose. I'm assuming that was the hose from the tank to the engine, what about the connector on the engine and the fuel hose to the carb? I take it that at some point in history this thing worked fine and put the thing on a plane. The other thing might be ignition advance but I would think that the tune up would have found that, but timing is normally checked at idle and it might not have shown up. I find it hard to believe that with all the work you've had done they havent run it at high RPM in a test tank. The other option is that it might be over-proped, but then it would not have worked in the past. I had a similar issue once on my rib and discovered that the fiberglass hull was full of water. Any chance that could be your problem?
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Old 13-12-2009, 10:18   #3
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Check the acceleration linkage and the membrane inside the bottom of the carborator. On my 15HP 4-cycle the diapraghm was broken so the motor failed to accelerate but idled fine - its a 15 dollar part.
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Old 13-12-2009, 10:26   #4
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Good point about the acceleration linkage. I once had a problem on my 15 hp yamaha. The linkage was mis adjusted and the cam was missing the plunger on the acceleration pump. The cam is not connected to the plunger, it only presses on it. If it is not positioned correctly it slips past it. A new carb should have fixed that but it's surely worth a check.
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Old 13-12-2009, 10:30   #5
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It sounds like fuel starvation. You said you replaced the fuel hose. I'm assuming that was the hose from the tank to the engine, what about the connector on the engine and the fuel hose to the carb? I take it that at some point in history this thing worked fine and put the thing on a plane. The other thing might be ignition advance but I would think that the tune up would have found that, but timing is normally checked at idle and it might not have shown up. I find it hard to believe that with all the work you've had done they havent run it at high RPM in a test tank. The other option is that it might be over-proped, but then it would not have worked in the past. I had a similar issue once on my rib and discovered that the fiberglass hull was full of water. Any chance that could be your problem?
I did not replace the fuel hose that's inside the engine cover - I'll try to verify its condition.

Dink is on davits all the time and no indication of a saturated hull. Since I've owned it the engine has not worked right so I can't say if it ever planed or not. But I would suspect that 15hp on this dink would do just fine.

The outboard mechanic who was a go-between to the repair shop claimed that they had the engine "screaming" in the test tank once and only once. That was in his tank - the repair shop was not able to get it to perform at their shop and they supposedly called Yamaha for help. After the shop got done, he and his buddy got it running in his tank, or so he claimed. Then when they brought it back and installed it on the dink we were back to slow city....
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Old 13-12-2009, 10:34   #6
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Good point about the acceleration linkage. I once had a problem on my 15 hp yamaha. The linkage was mis adjusted and the cam was missing the plunger on the acceleration pump. The cam is not connected to the plunger, it only presses on it. If it is not positioned correctly it slips past it. A new carb should have fixed that but it's surely worth a check.

Good point - I'll check that. Thanks!

BTW, this engine WILL NOT allow me to rev the engine using the tiller throttle unless the engine is in gear. Is that normal? I have to take the cover off and rev the engine by moving the linkage by hand. Then it revs fine.
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Old 13-12-2009, 10:38   #7
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In a shop they often use a test prop in a tank, it provides a load but not nearly what you might get on a real boat. My yamaha 15 hp will plane my 10ft rib with about 600 lbs on board, Total weight approaching 900 Lbs. 115 for the engine, 135 for the rib plus fuel and required equipment. When the hull was full of water (I estimate no more than 150 Lbs) it would not put us on a plane and gave us the same symptoms you describe. How much does your rib weigh fully loaded? It may be that you need to go to a slightly lower pitched prop to allow it to get you over the hump and onto a plane.
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Old 13-12-2009, 10:40   #8
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The high speed lockout in neutral is normal for this engine.
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Old 13-12-2009, 11:10   #9
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An engine with fuel starvation will often rev up under no load conditions. Interesting that they got this thing to rev up once in the test tank but only once. If they used a test prop this could be close enough to no load conditions if you were getting some fuel but just not enough for your load. I take it that they've done a compression test.
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Old 13-12-2009, 11:25   #10
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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.
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Old 13-12-2009, 11:28   #11
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Quote:
Originally Posted by markpj23 View Post


I've had it to the shop (without success) and after many $$ here's what has been done so far:
- new ignition coils
- new flywheel sensor
- new carburetor
- repaired the engine fuel pump (rubber diaphragm had been leaking)
- new plugs
- "tune up" whatever that means..
- new fuel hose
- new fuel tank

The outboard shop said they were stymied.... well DUH it's not fixed.

Before I go throw $90 / hr at another incompetent shop, is there something I should check?
That is a lot of stuff for the exact same problem.

I'll have to sleep on it.

Maybe someone will have the solution while I sleep..........
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Old 13-12-2009, 12:20   #12
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I would put that sensor back on....

Quote:
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.
I had a 9.9 that seized due to a sudden oil leak (I had checked only a few hours before. It had a sensor, but it malfunctioned. I hope to save you my grief.

Separated e-10 can also cause this symptom (low power).
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Old 13-12-2009, 23:22   #13
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RUN IT OFF AN NEW GAS TANK WITH NEW FUEL LINES

it can be the carb not rebuilt right

i would also do a compression check and read the spark plugs and check for spark
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Old 14-12-2009, 00:01   #14
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Oil. Either a leak or a malfunctioning sensor. I'm going through the same thing right now. I have a bad leak somewhere. If I add oil, it runs great. Within 1 hour the oil leaks out, and the engine drops down to idle.
Check this first, I think this is your problem.
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Old 14-12-2009, 00:10   #15
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Quote:
Originally Posted by markpj23
Yamaha 15hp 4-stroke outboard (F15ESHY model) starts and idles fine, but will NOT respond to wide open throttle and will not get the dink up on plane. When I goose it, the engine sounds like it's bogged down.... low growl. I can put along just fine, with the engine a few hundred RPM above idle, but it makes no power and can't begin to get the dink on plane. (11ft Achilles RIB)
I had the same problem with a Honda 4 stroke. It's that stupid ethanol Mine started getting worse with each start up. I ended up pulling the jet out of the carburetor and cleaning the crust out of it with a wire from a wire brush.

It worked great for about 10 more times then I had to do it again. The scary part was I was afraid I was going to drop the jet in the water. So I went and bought 2 spares. I ended up using one but sold the motor with one of my other boats.

Now I run a two cycle and use new gas every time I go on a cruise.
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