Marine 40hp 2-stoke loses revs and cuts out after starting

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11855

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Hi folks, I took my boat out of winter storage last weekend and brought it to my drive way with water tank to allow me to start my 2004 Mariner 40hp 2-stroke. I had run the fuel off before putting it in the shed. It started on first turn of the key and appeared to be running fine last Tuesday. On Thursday I started it again and recorded a video to share with a friend and again it was running fine as per Engine running for Steven

However on Friday I started it again and I noticed it didnt seem to be idling well and would start to lose power and cut out. I tried again today and the same thing. As it was loosing revs if I push on the key to prime and pushed up the throttle I could keep it going but as soon as I pull back on the throttle after a few seconds it would start to lose revs and cut out as shown here
Engine cutting out

It seems to be a fuel starvation type issue. Any idea, I removed and clean the plugs. The only thing I did between Thu and Friday was I add about 10 liters of unleaded to the 25 liter Quicksilver tank as there wasn't much fuel in it. I got the 10 liters from a 20l Jerry can I filled from a service station about 3 weeks ago.
 
Possibly a blocked idle jet. Pouring the new fuel into the tank disturbed muck in the tank that is now in the carb. The other option is dirty new fuel caused an issue, but either way it points to the carb.
Finally, it was petrol purchased and not diesel .....
 
agree, pilot / idle jet blocked. May not be fuel, if it was stored in a damp garage could be aluminium corrosion salts forming, either way look at carb and fuel delivery
 
I always check the basics first so I'd try running with the cap off the fuel tank to check it's breathing ok. I'd also pour out the fuel in the tank and try some completely fresh. Modern petrol goes off very quickly and the boat may be drawing stale fuel. Then fuel filter and obviously check plugs as they're simple to do anyway, and then i'd run some carb cleaner through the carbs and then if all else fails, start taking the carbs apart to clean jets etc.
 
Folks, quick update. The fuel I used last Friday to top up the quicksilver 25l tank was bought on 14 April from Circle K. It was stored in a 20l new Jerry can in a garage which could indeed have been damp. I then used a plastic 10l fuel tank to transfer the fuel from the jerry can in the garage to the boat. The 10l was empty.

could it be as simple as 6 week old unleaded causing my woes?

this evening I removed and cleaned the fuel filter and I could not see any dirt. I also emptied the 25l and added some fuel from another Jerry can with same results. I also removed and cleaned the spark plugs (new last summer)

@Fire99 can you recommend a carb cleaner. Unusually order marine stuff from marineparts.ie? I don’t feel confident about stripping the carb myself so want to try everything I can before turning to a marine specialist.

how about STP Carb Cleaner


perhaps I should try carb cleaner and 10l of fresh fuel
 
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I struggle to understand why outboards as so super sensitive to things like stale fuel. I have never had such issues with my garden equipment in 4 and 2 stroke. Can someone enlighten me :)
 
11855 said:
I struggle to understand why outboards as so super sensitive to things like stale fuel. I have never had such issues with my garden equipment in 4 and 2 stroke. Can someone enlighten me :)
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Wider rev range, higher output/cc means fancier carbs are needed means more sensitive. It's like comparing a car engine to a motorbike engine - same idea, very different execution.
Add in stale and/or waterlogged fuel and you have an issue - hence much-used outboards (and motorcycles, and strimmer and chainsaws) generally being very reliable - it's the idle ones that go wrong.
 
6 week old fuel will not be the problem. I have petrol over 2 years old and no issues and certainly not on an older 2 stroke.

look at the gasket between the carb body and the float chamber. If that is sucking in air that will cause exactly the issue you are having.

people so often believe the old fuel babble and that is seldom the case
 
11855 said:
I struggle to understand why outboards as so super sensitive to things like stale fuel. I have never had such issues with my garden equipment in 4 and 2 stroke. Can someone enlighten me :)
Click to expand...

I don’t think they are more susceptible. People just jump to that conclusion and it is seldom the issue. It causes people to throw away perfectly good fuel which of course is very difficult and expensive to dispose of properly.

do you honestly think all those big petrol boats on moorings ditch their petrol at the end of the season. And if they did how and where
 
11855 said:
Folks, quick update. The fuel I used last Friday to top up the quicksilver 25l tank was bought on 14 April from Circle K. It was stored in a 20l new Jerry can in a garage which could indeed have been damp. I then used a plastic 10l fuel tank to transfer the fuel from the jerry can in the garage to the boat. The 10l was empty.

could it be as simple as 6 week old unleaded causing my woes?

this evening I removed and cleaned the fuel filter and I could not see any dirt. I also emptied the 25l and added some fuel from another Jerry can with same results. I also removed and cleaned the spark plugs (new last summer)

@Fire99 can you recommend a carb cleaner. Unusually order marine stuff from marineparts.ie? I don’t feel confident about stripping the carb myself so want to try everything I can before turning to a marine specialist.

how about STP Carb Cleaner


perhaps I should try carb cleaner and 10l of fresh fuel
Click to expand...

Hello mate..

I think the stale fuel issue may be a bit of a red herring. Maybe I misread your post but I thought you had left a small amount of fuel in the tank for months and months and then topped it up. A virtually new motorbike that I had suffered as a result of the same, so I always like to discount it. Unfortunately with the price of fuel these days, a tank of fuel can end up more expensive than a carb strip.

Any aerosol carb cleaner that you can spray into the intake would be fine. They're mostly all the same.. Solvents to break down any gum. 2 strokes by nature do get a bit gummy when left because the oil/fuel mix is slightly stickier than the pure petrol of a 4-stroke but other than each one having it's own 'personality' for starting they're pretty simple little things. I run a 1991 10hp for my tender and wouldn't have anything else.
 
hi folks, I have a marine mechanic lined up to take a look at the engine. As always I greatly appreciate the input. I have learned loads from the feedback on this forum and the boat was a great distraction during Covid. I will let you know when my engineer finds
 
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