Outboard dying unexpectedly ?

[nathan007]

I have a 08 Yamaha f15, runs great all the time, until yesterday when during a two hours ride it started dying under power, and would start back up after, then die again after 3 to 5 minutes running. Really looked like fuel starvation (no misfire, no knocking, just throttle bogging down in a flash then try to keep going and just die off)

Now, engine was hot (running two hours straight) but exhaust water was normally warm (not burning, not cold)

I suspected the coil but then when I made it to the dock I noticed my fuel primer bulb line was installed backwards (arrow towards tank) I did not get a chance to re-run it, but could it be possible it would allow the engine to run normally at all rpm's, but after such a long ride just cause issues??

[a64pilot]

Fuel primer installed backwards shouldn't have allowed it to run at all as it has a one way valve of course that won't allow back flow, seems yours may be damaged.
99% of the time bad running issues are traced to bad fuel gunking up the carburetor, but in your case I'd suspect the fuel pump diaphragm has a tear and it's leaking air and not pumping fuel well. It may be the backwards primer bulb may have damaged it too, easy fix though if you can get a diaphragm, take the pump apart if the diaphragm is damaged you should be able to see the tear.
Another way to diagnose a bad fuel pump is with a properly installed and functioning fuel bulb, it will run fine as long as you keep squeezing the bulb, but die soon after you stop, this is of course because your the fuel pump as long as your squeezing the bulb

[DeborahLee]

When was the last time the fuel filter was changed? Is it new gas or last years gas?

[nathan007]

I had just filled up prior to going out, so fresh, premium gaz plus a few drops of seafoam to keep it nice.

I will need to recheck the fuel pump with a vacuum tester, but what I worry about is the fact that the engine runs perfectly fine , idle to wot, but will start to bog and die within minutes (on my returne ride)

Next weekend I will go try it out see how it runs , if I have the same issue after my usual runs, if it does die will see if I can keep it going by priming it

The fuel filter is the small basket type directly on the inlet in the engine, it was filled with fuel when it died (trying to figure out wft is going in), its been cleaned during my spring tuneup

[GrowleyMonster]

You did open the fuel tank vent, right?

[Adelie]

GM you beat me to it.

[GrowleyMonster]

Oh and yeah, try it with the squeezybob turned the other way, if opening the tank vent doesn't fix it. It sounds like it is installed correctly, though, in spite of the arrow. It won't pump, turned the wrong way.

[nathan007]

Yes, I did open the tank vent
The bulb was reversed because I remember it being closer to the engine before, and it can explain why when I primed it the bulb would kind of feel collapsed and never get hard... But hey the engine ran fine!!

I hope I did not damage the fuel pump diafram,

[DeborahLee]

Check inside the engine for a fliter. My 8hp Yamaha had one, never really noticed it and I rebuilt the carb twice in 7 years. This year it finally gave me grief and I found it.

[ingrid75]

Okay, here is a wierd one that sometimes happens: the outboard engine block is two castings bonded together. Sometimes an older engine, especially if it has run hot, will, when it warms up and expandes, allows a gap to open between the halves This allows air to enter the crankcase and leans out the mixture to the point where the engine stalls. Then, when the engine cools, the gap disappears and the engine runs well for a few minutes until it warms up and gap reappears and it stalls again. The way to check this is to spray the casting seam with WD40 just as the engine starts to stall. When you spray the area with the gap, the engine will run well again for a few seconds. Good luck.

[Cadence]

I think it is a simple as the one way valve in the primer bulb? It was such open then closed?

[roygee]

Originally Posted by nathan007

I have a 08 Yamaha f15, runs great all the time, until yesterday when during a two hours ride it started dying under power, and would start back up after, then die again after 3 to 5 minutes running. Really looked like fuel starvation (no misfire, no knocking, just throttle bogging down in a flash then try to keep going and just die off)

Now, engine was hot (running two hours straight) but exhaust water was normally warm (not burning, not cold)

I suspected the coil but then when I made it to the dock I noticed my fuel primer bulb line was installed backwards (arrow towards tank) I did not get a chance to re-run it, but could it be possible it would allow the engine to run normally at all rpm's, but after such a long ride just cause issues??

I have a Yamaha 20, they changed the fuel tanks and hookups. The company issued a recall, I was issued two new tanks and three gas hoses over a 9 month period. The hookups leaked fuel and sucked air, which caused the engine to die. Another problem is the counter was loose and it would act like yours, until it completely fell off and left me stranded in Matagorda Bay. .

[Dean Paul]

This post reminds me of the time when my Palmer 4 cylinder inboard would stop after a few minutes running. Wait a few minutes then it would start up again. Discovered the tank vent on the transom was plugged with years of polishing wax accumulation. This caused a vacuum in the tank. Cleared the vent....perfect performance since then. Just had to share.

[zedpassway]

Originally Posted by nathan007

I have a 08 Yamaha f15, runs great all the time, until yesterday when during a two hours ride it started dying under power, .......

Fuel tank vent switch will definitely do it. I've had that happen. Stalls right away. Seems such a small thing.

Running high ethanol in the gas(or any) can do it. The government keeps increasing the ethanol content, and there is a level where even engines that will run on ethanol gas won't anymore.

[Cadence]

Originally Posted by zedpassway

Fuel tank vent switch will definitely do it. I've had that happen. Stalls right away. Seems such a small thing.

Running high ethanol in the gas(or any) can do it. The government keeps increasing the ethanol content, and there is a level where even engines that will run on ethanol gas won't anymore.

You mean corn syrup? I feel sure it may be practical some time when as much research pans out as has gone into gas. A renewable source would be great. Until then buy white gas at the marina I think.