Outboard cutting out when the choke is pushed in.

[Seven Spades]

My outboard is cutting out when I push the choke in. If I keep the choke on it runs rich but I have reduced power. I took it to be serviced, carburettor cleaned, spark plug replaced etc, but it has made no difference.

What are the possible causes of this. It could be that the mechanic did not strip down and clean the carburettor or is could be something else. I would welcome suggestions to possible causes.

 

[Roberto]

I had the same on mine I used those carburetor cleaning sprays, by memory some went in the tank with a little petrol inside, the rest sprayed in the carburetor air intake while the engine was running. Immediate effect
(Mine was 2 stroke, if that makes any difference)

 

[Seven Spades]

Mine is a 4 stroke and the mechanic says he has run cleaner through it but did not strip it. He thinks it is E10 fuel.

 

[Momac]

What fuel are you using?
I find my small avery old outboard and not so old lawnmower start easier and run better on E5 premium fuel. Also fresh fuel always improves starting and running compared to older fuel.
My car deals perfectly well with E10 fuel but older technology motors with carburettors don't seem to like it.

 

[Roberto]

Mine is a 4 stroke and the mechanic says he has run cleaner through it but did not strip it. He thinks it is E10 fuel.

That can definitely be another cause, I had to use petrol with heavy ethanol content and it was a nightmare, as soon as I could get back to premium petrol it all went back to normal.

 

[The Q]

If you exclude E10 then the traditional fault that causes this is the main jet is blocked / partially blocked..

 

[Steve65]

The problem is a blocked idle jet caused by leaving fuel sitting inside the carburettor.
If the outboard is stored correctly with no fuel in the carb e10 fuel will not cause any issues whatsoever

 

[Momac]

If the outboard is stored correctly with no fuel in the carb e10 fuel will not cause any issues whatsoever

I always stop the outboard engine at the end of a days use by turning the fuel tap off and let it run out of fuel.
However E5 premium fuel did make a difference to easier starting and better running in my case .But the engine does date from 1966 which might make a difference. It possibly has more to do with the premium fuel being slightly higher octane rather than the ethanol content.

 

[syfuga]

Sounds to me like blocked slow running. Strip the carburettor and clean/blow it through

 

[wallacebob]

Slow running jet blocked by particulate caused by E5/10. Strip, clean and use additive in fuel. Ethanol is hygroscopic, and can cause corrosion of float chamber components. This creates small salt like particles. Well known issue, get additive at Halfords or garden centres.

 

[Steve65]

I always stop the outboard engine at the end of a days use by turning the fuel tap off and let it run out of fuel.
However E5 premium fuel did make a difference to easier starting and better running in my case .But the engine does date from 1966 which might make a difference. It possibly has more to do with the premium fuel being slightly higher octane rather than the

I always stop the outboard engine at the end of a days use by turning the fuel tap off and let it run out of fuel.
However E5 premium fuel did make a difference to easier starting and better running in my case .But the engine does date from 1966 which might make a difference. It possibly has more to do with the premium fuel being slightly higher octane rather than the ethanol content.

A 1965 engine will not be set up to run ethanol

 

[VicS]

Mine is a 4 stroke and the mechanic says he has run cleaner through it but did not strip it. He thinks it is E10 fuel.

Try E5 or Esso Synergy+ 99 which is ethanol free ( except in the SW, N Wales, N of England and Scotland).
More than likely you will have to properly clean the carb, especially the slow running jet and passages

 

[Concerto]

Modern petrols only have a shelf life of 3 months, so old fuel is most likely to be the problem. Once you have solved the running problem, I would advise changing your fuel to Aspen 4 (Aspen 2 for 2 strokes). Aspen is a synthetic petrol that has a shelf life of over 3 years, so should avoid further problems in the future. It is slightly more expensive, I bought 5 litres for £20 last week, but when you consider how little petrol you use in an outboard, it does mean you will not waste any. It also comes in plastic containers to ensure the life of the fuel. Just check where your nearest stockist is. PS It is also good for lawn mowers and chain saws.

Aspen 2 | Aspen 4 | Premixed Petrol | Aspen Fuel

 

[Slowboat35]

My Mariner 4Hp had this problem pre E10 petrol. Diagnosis is pretty clear - blocked main jet.
It was caused by degradation of the fuel pipe between the tank and carb causing tiny (and I mean tiny) crumbs of black plastic to lodge in the main jet. It was easily if tediously cleared by removing the carb, partially dismantling it and blowing the passages clear with an airline. Trouble was, as the entire inside of the pipe was degrading there were thousands more bits waiting to do the same.
Suggest you carefully clean out the tank, re-new fuel lines and fit a small inline filter close to the carb.

Carb cleaner will have no effect if this is the problem.