Strange behaviour from my outboard.

[ash2020]

I have a lovely old Mariner 2HP 2 stroke outboard on my tender. Anyone who has owned one will know they are practically bombproof. However, now it has taken to cutting out after a couple of minutes running. Starts very well, runs nicely but after about 100 yards it slows down and dies. Almost as if the air vent was closed. (I may have answered my own question, maybe it's blocked). Any other ideas? Brand new fuel BTW.

 

[veshengro]

Fuel starvation perhaps? It starts and runs when the Carb is full and then dies as the flow ceases.

When finished using my Outboard I turn the fuel off and run the Carb dry, my engine a 4 hp Mariner 2 stroke runs a little more than 100 yards ( depending on conditions) but it then dies in a similar manner to yours

 

[snowbird30ds]

I've had the pickup inside a portable tank split so a few pumps on the bulb and it runs but then doesn't have enough suck to draw more fuel up, it only played up when half empty as that was the level of the split.
Replaced pickup and it was fine.

 

[ash2020]

Fuel starvation perhaps? It starts and runs when the Carb is full and then dies as the flow ceases.

When finished using my Outboard I turn the fuel off and run the Carb dry, my engine a 4 hp Mariner 2 stroke runs a little more than 100 yards ( depending on conditions) but it then dies in a similar manner to yours

Thank you. I'm pretty sure it will be fuel starvation. I will turn the fuel off and time how long it runs.

 

[ash2020]

I've had the pickup inside a portable tank split so a few pumps on the bulb and it runs but then doesn't have enough suck to draw more fuel up, it only played up when half empty as that was the level of the split.
Replaced pickup and it was fine.

That's a good point. Although it is an integral fuel tank, I guess it has a pump. Maybe the diaphragm's gone. Thanks.

 

[Bobc]

Float needle sticking

 

[Stemar]

I don't know if the Mariner does, but some outboards have a little filter build into the tap assembly. This being partially blocked could give your symptoms.

A more remote possibility that happened to me on a Tohatsu 3.5, which is basically the same engine - typical fuel starvation symptoms, but it turned out to be a corroded connection of the coil earth to the block. A good clean and everything was fine again.

 

[ylop]

I've had the pickup inside a portable tank split so a few pumps on the bulb and it runs but then doesn't have enough suck to draw more fuel up, it only played up when half empty as that was the level of the split.
Replaced pickup and it was fine.

I think the OP's engine is gravity fed from the tank.

 

[neilf39]

My tohatsu did that when the cooling channels got blocked up in the head so it got too hot and seized. If left to cool it would then work again. Had to disassemble and clear it all out. The channels were well blocked. Has worked fi e since doing that.

 

[Mark-1]

Coils work better cold so wouldn't rule out the coil but perhaps the last thing to check once the carb has had a good clean.

But agree carb is more likely culprit.

Take the petrol tank lid off to rule out the air vent in the cap?

Sure you've got plenty of gas in the tank? I reckon these engines are pretty sensitive to low fuel, easy to fill it brim full to be sure.

 

[greeny]

Restriction in fuel supply. First strip carb and check float and needle and the seat are not gunged up due to modern fuels E5 e10. Then check that tank filter located above fuel on/off valve is not gunged up. Fuel runs out after a couple of minutes running tells me that the bowl is full on starting but is not being re-filled fast enough when engine is running so eventually runs dry. Of course try running it without the filler cap on first, as others have suggested, to make sure its not the air vent in the cap that is blocked. I would expect that to take more than a couple of minutes to have adverse effect though.
The other thing you've not mentioned is the position of the choke in all this. If its running ok on cold start with full choke, then stops when you reduce choke setting that may indicate blocked jets and passages in the carb. Its not a modern 4 stroke with all the small orifices so should be easy to clean in this event.

 

[HunterWanderer]

Also could just be the spark plug. Insulation breaks down when hot.

 

[Mark-1]

....and the little filter in the tank over the fuel tap.

 

[footsoldier]

Deleted

 

[Beneteau381]

I've had the pickup inside a portable tank split so a few pumps on the bulb and it runs but then doesn't have enough suck to draw more fuel up, it only played up when half empty as that was the level of the split.
Replaced pickup and it was fine.

They don’t have a separate tank and no pickup. The tank is integral on top of the engine, gravity fed, no pump.

 

[Beneteau381]

That's a good point. Although it is an integral fuel tank, I guess it has a pump. Maybe the diaphragm's gone. Thanks.

Nopump

 

[littledancersadhu]

I would strip the carb, clean it out, high pressure air to blow out the jets etc.

 

[Fantasie 19]

Also could just be the spark plug. Insulation breaks down when hot.

+1.. had a Tohatsu that would run sweet as a nut for 5 or 10 minutes and then die, changed the plug and all good