2 stroke outboard problems

[blackrose]

I have a Mariner (Tohatsu) 2 stroke 4hp outboard and it cut out today while I was crossing the river. A bit scary since the river's moving quite fast today. It's a second hand engine and I don't know it's history. I gave it a service when I got it 6 months ago including a new spark plug.

 

I usually use it just to cross the river every day after warming it up for a couple of minutes. Because of all the short trips I thought it might be a good idea to take it for a proper run and blast any coke out, which was fine until I rolled off the throttle and it cut out in the middle of the river. I eventually managed to get it started again but it will only run at medium to high revs. At low revs it just cuts out.

 

Anyone have any ideas? I checked the idling setting and that seems ok. Is it likely to be the plug, or a clogged fuel filter which can only suck fuel through at high revs, or could it be an air leak getting into the fuel system?

 

Thanks

Edited January 16, 2011 by blackrose

[Joss]

ok how old is the fuel in the tank ?

check the air filter

fuel filter

plug

if they are ok try some new fuel

if its still playing up i would go for the carb give it a good clean out if you can get to a compressor blow the jets out just in case its got some muck in .

good luck

[blackrose]

ok how old is the fuel in the tank ?

check the air filter

fuel filter

plug

if they are ok try some new fuel

if its still playing up i would go for the carb give it a good clean out if you can get to a compressor blow the jets out just in case its got some muck in .

good luck

 

Thanks. The fuel is only a few weeks old. Interesting that it only happened after I gave it a good blast - or perhaps just coincidence?

 

I'll have to check it tomorrow or one day this week when it's not raining.

Edited January 16, 2011 by blackrose

[1066]

It sounds like a blockage in the idle jet in the carburettor. I recently had a similar problem with a Honda outboard that wouldn't run at anything less than about 2000rpm!

 

I bought an ultrasonic cleaner from Aldi for around £20 which did a great job of cleaning all the muck out of the carb.

Edited January 16, 2011 by 1066

[blackrose]

It sounds like a blockage in the idle jet in the carburettor. I recently had a similar problem with a Honda outboard that wouldn't run at anything less than about 2000rpm!

 

Is that an easy fix or does it mean stripping the whole carb?

[1066]

Is that an easy fix or does it mean stripping the whole carb?

 

I stripped the carb. Whether that is the only way to do it, I don't know. It just seemed the best way at the time.

[blackrose]

I stripped the carb. Whether that is the only way to do it, I don't know. It just seemed the best way at the time.

 

Thanks. I've stripped carbs on 2 stroke bikes before so I'll give it a go.

 

I'll check the plug and filters first.

[Keeping Up]

One other possibility is a problem with the magneto being unable to produce a voltage high enough to spark when the engine is revving hard, assuming it has one. I remember having this problem on a moped, many years ago, and it was that the condenser (that's what they called the capacitor then) had failed so that the points had been sparking badly, until they deteriorated and the spark failed.

[blackrose]

One other possibility is a problem with the magneto being unable to produce a voltage high enough to spark when the engine is revving hard, assuming it has one. I remember having this problem on a moped, many years ago, and it was that the condenser (that's what they called the capacitor then) had failed so that the points had been sparking badly, until they deteriorated and the spark failed.

 

Having stripped the carb last Saturday and found it to be perfectly clean I'm starting to think the problem might be electrical. I blew out the jets abnd put it all back together but it still won't idle properly. It runs fine revving hard but not at low revs. I checked the spark and it's there - but perhaps a bit weak?

Edited January 24, 2011 by blackrose

[steelaway]

Having stripped the carb last Saturday and found it to be perfectly clean I'm starting to think the problem might be electrical. I blew out the jets abnd put it all back together but it still won't idle properly. It runs fine revving hard but not at low revs. I checked the spark and it's there - but perhaps a bit weak?

 

 

Hi

 

The next thing I would check is the crankshaft seals. If these are worn you will be pulling air into the engine and until there is enough petrol to overcome the weak mixture it wont run properly.

Have a feel at the crank for up and down movement, if there is any the bearings are worn along with the seals. First check the side that is most open to the atmosphere - generator side?

 

Alex

[blackrose]

Thanks Alex, would worn crankshaft seals still allow the engine to run normally at medium to high revs?

 

Mike

[Keeping Up]

I see I missed the word "except" from my earlier post, which should have said "the magneto being unable to produce a voltage high enough to spark except when the engine is revving hard" but I think you understood what I was trying to say.

The suggestion about crankshaft air seals is a good one. Another one of my succession of ancient mopeds when I was a student, had this fault. I don't particularly remember it showing up as a low-revs problem in my case; what I do strongly remember however is that my logical student brain said "too much air is the same as not enough fuel" so I cured the problem by giving it a small amount of choke to richen the mixture. By constant and careful adjustment of the choke I could get that 'ped to travel at least 10 mph faster than it had done when everything was normal. In fact it went so fast that it proved dramatically the truth of the prophecy engraved on the small plate by the speedometer, which said (in French) that the engine would explode if I exceeded 60 kph.

The point of this rambling story, is to wonder whether you can try giving it some choke when it is running badly.

[XAlan W]

Having stripped the carb last Saturday and found it to be perfectly clean I'm starting to think the problem might be electrical. I blew out the jets abnd put it all back together but it still won't idle properly. It runs fine revving hard but not at low revs. I checked the spark and it's there - but perhaps a bit weak?

I think you will find if the outboard is not too old is that the ignition is electronic [no points/condenser] & that if it is the problem, it is a fit a new unit job. also check the fuel pump for air leaks [if it bolts to the motor check the gasket between pump/crankcase. If it is remote check the pipe between pump & crankcase. Also check pump diapham for slits/pin holes, also make sure the little flappy bits[fuel valves are flat & not wrinkled] hope this helps.

[Sir Nibble]

Obstruction in the exhaust?

[steelaway]

Obstruction in the exhaust?

 

 

Hi

That was going to be my next suggestion. Also the air filter.

You could try applying the choke 'abit' as mentioned.

 

Alex

[blackrose]

Thanks all. It generally needs some choke to start but I'll try giving it some choke to see if it will idle - if it does then at least it would give some clue as to the problem.

 

I was kindly given the used outboard along with an aluminuim punt by the landlady at my new mooring in order to get on and off the island, but when I first checked the tank I could see that there was no 2-stroke oil in the fuel. Some idiot had filled it up and run it for a few days without oil and to be honest I was surprised it was still running. I suspect premature wear has occured somewhere - I was just thinking piston & bore, but I guess it would be crankcase bearings too.

Edited January 25, 2011 by blackrose

[blackrose]

I took it to Penton Hook marina who service outboards and it turned out to be a faulty coil on the magneto as Alan (Keeping Up) suggested.

Edited January 28, 2011 by blackrose

[Keeping Up]

Glad it's sorted (I always knew my experiences on mopeds would be useful one day)