Mariner 3.3hp two-stroke problem

[boatsRus]

I have a 16 year old Mariner 3.3hp two stroke outboard (standard shaft). Last summer, it died mid-cruise so I brought it home and thoroughly cleaned the carb, replaced the piston ring, oil seals, gasket, spark plug, fuel tap and filter, and fuel cap. It still won’t run properly (although it starts occasionally and runs for a few seconds). There is a good strong spark and the fuel is new. I have run out of things to try. Any ideas gratefully received. Alternatively, does it have a value as a non-runner??

 

[Mistroma]

I have had one of those for years and never had any major problems. It sounded like a fuel problem but you've done all the obvious stuff, including the filter inside the tank. I cleaned that filter a couple of years ago and it was pretty dirty. Many people don't even know that filter exists.

Changing the seals and piston ring seems like a lot of work unless you had good reason. I assume you tried all the obvious fuel and spark things first before getting more desperate.

I assume you've filled the tank, disconnected the hose at the carb. and fuel flows out of the end as soon as you open the tap. It's a very easy check to collect a few hundred mls in a beaker and cycle back to the tank. If you've done that then fuel is reaching the carb. bowl.

The next step might be to open the drain on the bowl and collect fuel pouring out in a steady stream. I'm assuming you have already done that as well.

I did once have a similar problem but resolved it very quickly. I checked for a spark, fitted a new spark plug and that didn't help. I carried out the above checks and then removed the carb. as you've already done. The problem just seemed to be a sticking float that prevented flow of fuel. It was quite a while ago but I didn't buy a new carb. or even a float. A thorough clean did the job but took 2 attempts before it no longer stuck. It was still going strong in 2019 and hopefully in 2022.

Sorry not to be much help. I suspect I've just outlined things you've already done. It's a great little engine, light and adequate power. I imagine someone would buy it as a non-runner, even for spare parts. I'd be surprised if the buyer couldn't get it running again.

 

[boatsRus]

Thanks Mistroma. The reason that I stripped down as far as I did was that a professional outboard engineer told me that he thought the problem was the reed valve. Needless to say, it was fine, but I changed the other bits anyway!!

 

[Mistroma]

Thanks Mistroma. The reason that I stripped down as far as I did was that a professional outboard engineer told me that he thought the problem was the reed valve. Needless to say, it was fine, but I changed the other bits anyway!!

I makes sense. It's such a good engine that I'd have stripped it as well if the obvious stuff didn't produce a result. I remember proving it was a fuel problem on an outboard in my youth. One person started it and I sprayed fuel into the carb. using small bottle. It was a long time ago and might have been an old perfume bottle with 2 stroke mix. Too far back to remember details but it did keep running on repeated squirts. I think I replaced the carb. and all was well. Expensive route and only worth it if you are 100% certain it's the carb. but can't identify the reason.

I did wonder about the reed valve but assumed you'd examined and cleaned that area when replacing the rings. The obvious things are spark, fuel flow, jet and reed valve. Pretty much has to be one of these as main culprit with possibility of others contributing.

 

[LONG_KEELER]

Compression test possibly ?

Teaspoon of fuel in plug hole ?

Best of Luck.

 

[Blueboatman]

Exactly What Mistroma wrote
Just work through again ?
the fuel filter check
And the float function check
Then put a bit of fuel in an old spray cleaning bottle, remove the air filter and spray fuel mix directly into the carburettor . It should fire up and run till it has used up that squirt of fuel mix . Indicating all the relevant bits are in good enough fettle


last ‘other thing’ to check is that the exhaust hasn’t somehow got clogged I suppose
And that the fuel tank cap can breath …

after that it fed a bit more forensic on the ignition performance side
And , give the flywheel a wiggle whilst the gearbox is in gear and you are holding on to the propellor -OBVIOUSLY REMOVE THE SPARK PLUG Cap donut can’t fire up and chop yer fingers off ? /- this last test is to make sure the flywheel key hasn’t sheered “ somehow” and shifted the ignition timing.. v v unlikely but worth crossing off ! (Quite common on lawnmowers that bang into obstacles , for example)

 

[jwilson]

I had a heavily used Mercury 3.3 that steadily got more difficult to start and keep running despite all the usual carb cleaning/ filter/ fresh fuel/ new plug jobs. Eventually took it to local outboard service shop, who pulled the starter cord and said ".... compression too low". They had another similar o/b there, and it was obvious that mine had much lower compression.

Too much effort to fix so sold it for parts and started using my spare outboard, a mechanically identical Tohatsu 3.5 that also had clearly much more compression - as it had probably only run a few hours from new - bought just before 2-strokes were banned from sale and kept in cellar as a backup outboard.

 

[Bobc]

The float needles are renowned for corroding and sticking. Have you changed that?

 

[seumask]

It may not seem obvious but I have found that the spark plugs are notorious on these small 2 strokes. Once your happy clean fuel is working its way through the Carb then a new spark plug is relativly cheap and quick to apply to the problem. I keep one on the engine for this reason.

 

[Skylark]

It may not seem obvious but I have found that the spark plugs are notorious on these small 2 strokes. Once your happy clean fuel is working its way through the Carb then a new spark plug is relativly cheap and quick to apply to the problem. I keep one on the engine for this reason.

+1

I have a Tohatsu which I’ve owned from new. It has very low hours but started playing-up a couple of years ago. Someone (probably on here) suggested plug. I didn’t believe it, especially as it appeared to have a good spark, but I’d otherwise run out of ideas so changed it. Problem solved ?

Well worth a try.

 

[jdc]

I have a Mercury 3.3, and it has had the same issue. Eventually, more out of desperation more than forensic work, I fitted a new HT ignition coil, and it ran reliably afterwards. Previously it would run for a few minutes and just stop, but sometime restarting for a while.