Outboard dying unexpectedly ?

[basssears]

Some good suggestions above. To see if your tank vent is clogged try cracking the fill cap a few turns as the engine is dying and see if it revives again.

But to be complete, can you give us a little more info?

Specifically, is outboard transom mounted or in a well? What were the weather conditions? No breeze, slight headwind, slight tailwind?

What I'm getting at is another side of the gas engine triangle (air, fuel, spark)... if you had a slight tail wind, which makes your apparent wind while motoring basically zero, could you outboard have been choking on its own exhaust?

I have Yamaha 8 in a well on a Nimble 20 and it took me a long time to diagnose this issue, finally had to install a blower in the well, very obvious this was the problem once blower was in as engine would start to bog down (especially with a slight following breeze) and as soon I turn on the blower I smell really strong exhaust smell and engine starts to run well again.

The above may not apply to your situation but there you go...

[Var Korall]

Fuel hoses may be deteriorated and collapsing on the inside layer, while the outside looks fine, most likely from ethanol.

[44'cruisingcat]

With the primer bulb the wrong way round, I'm surprised it ran at all!

[nathan007]

Thank you all for your input!!

The outboard is on a rib, so transom mounted, I had decend headwind but no waves since it was coming from shore.

The vent seems to work well (Yamaha outboard 24L tank,), if I close the vent in the evening, the following morning it will hiss when I crack it open once its been warmed by the sun.

I suspected water issues on ignition items , but I checked it twice and nothing was wet, everything dry, no water under the bonnet.

For now my guess would be issues with the fuel supply (fuel line reverse installed, somewhat running well this way), possible fuel pump diafragm issue (will test with vacuum pump and factory manual)

I'll check my spark plugs before starting it up see how they look. Sadly I can't do anything until next Saturday, so I'll research and pray its an easy fix!!!

[basssears]

Originally Posted by nathan007

The vent seems to work well (Yamaha outboard 24L tank,), if I close the vent in the evening, the following morning it will hiss when I crack it open once its been warmed by the sun.

Definitely try cracking the whole lid itself when the engine starts to sputter to see if that helps. My experience (and maybe it's just the tanks I've had) is that the vents generally only allow air IN, not OUT (if my tank looks like it's got some pressure in it I crack the fill cap itself to bleed off the pressure, or press down on my vent)...

-- Bass

[a64pilot]

Originally Posted by 44'cruisingcat

With the primer bulb the wrong way round, I'm surprised it ran at all!

I t should not have as of course a primer bulb just like a diaphragm water pump has two valves, one inlet, one exhaust, to get fuel to go backwards thru the bulb, it has to pass backwards through both valves.
If we were betting money, I'd bet no way could it have run with the bulb backwards, strong engine driven pump obviously.

[skipmac]

A couple of years ago my dinghy outboard starting doing the same thing. Would crank and run perfectly for a couple of minutes then sputter a bit then die. Was certain it was a fuel thing. Checked the hose, the bulb, the diaphragm, even cleaned the carb, no help. In the course of things I did check the spark. Pulled the plug, grounded it on the block and pulled the engine over and got a strong, blue spark.

After a few days and several hours of tinkering in desperation I put in a new spark plug and problem solved.

I had always thought plugs were more or less go or no go but apparently not. Had the same thing happen recently with another small engine.

[captaingregger]

Try replacing your fuel line with a pure rubber hose vs that vinyl synthetic garbage that a lot of the manufacturers are still using.

I had a similar issue earlier this year. Trouble shot for a few days before giving up and taking to to my outboard mech. He told me, "make sure you bring the fuel line and associated tank with you when you bring the engine to me." First thing he does before I even get the outboard out of my truck is take the fuel line and slice it open longitudinally. He peels it open to reveal almost complete clogging of gunk. He tells me that he sees that all the time. The manufacturers knew the the lines deteriorate from the inside due to the new E85 fuels but they wont' issue a recall. He swapped me out with a pure rubber line and viola', problem solved.

A month later same power loss started happening again. I took it to him and he said some of the gunk probably lodged itself into the carb so he rebuilt it for me for $35. He's known as the outboard motor guru here on Guam. Very nice guy indeed.

[hamburking]

Originally Posted by 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.

For me it was spiders in the vent hose. Those pesky spiders were finally able to completely plug the hole. I figured it out when I opened the filler cap, then was able to start the engine. Close the cap, and a couple minutes later the engine dies. I suspected a fuel problem, and noticed the plastic fuel tank was all "sucked in". I pulled off the vent hose from the tank end, put it between my lips and blew...at first nothing, then POP, sent those spiders for a ride. Ran fine ever since.

[CarlF]

You "just filled up" and then this started?

Even reputable fuel suppliers occasionally get bad fuel. In the US, the "brand" means nothing. Everyone buys gas from the same wholesalers (when did you last see a delivery tank truck with Mobil painted on it?)

And newer small four cycle outboard engines are very sensitive to fuel

[etterridge]

Originally Posted by 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.

Our newish Tohatsu 6 HP had a similar issue last winter and the cause turned out to be what Ingrid refers to (crankcase vacuum loss). In our case the fuel pump bolts had loosened slightly.

Some gasket sealant, a little loc-tite, and reinstall of fuel pump saw the problem resolved.

[nathan007]

I'm going there tomorrow, will check out and keep you updated!

[nathan007]

Well I checked my fuel pump with positive pressure And vacuum according to the shop manual, I may have a slight leak on the 'out' side, went for a 30 min test run anyway, everything was working fine..

I will try it again today to see if I can reproduce my issue, only change done since is putting the fuel line in the good direction!