Why are 2-stroke engines so consistantly unreliable

We run a pair of two stroke outboards. Both are incredibly reliable. The Tohatsu 9.8hp is as old as the hills but still runs great. Its all about carbs on a two stroke. Keep them clean, run good fuel. Never use old fuel. Add an additional fuel filter if you can. We run an extra large filter on the fuel line between remote tank and the engine. Run them regularly. Keep the plug gapped perfectly. Having once owned a brand new Mercury 6hp four stroke, I will never go back to another four stroke. Hard to start when warm, heavy as hell and sounds like a lawn mower!
 
BurnitBlue said:
Well I certainly do not get on with 2-strokes either. I did not buy a 4-stroke because they are too heavy for an IFboat among other reasons. .
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A four stroke outboard is not that much heavier than a 2 stroke one surely? I mean how much difference is, say, 4or 5 kgs going to make on a boat that weighs over a tonne? By “IFboat” I assume you mean International Folkboat. Correct? What’s her displacement?
 
I've had "issues" with a few 2Ts over the decades. Many of the issues are common with the 4T issues I've also had, apart from the fact that 2Ts can suffer from oiling-up of the spark plug/s which is much less of a problem with 4Ts. It tends to mean that if a 2T is being a bit of a bugger to start, perhaps due to a poor battery, poor electrical connections, poor fuel flow etc. then the 2T will oil-up with repeated attempts to start it which means that you then have another reason why it won't start. :ambivalence:

Richard
 
I like my nice, lightweight, reliable two strokes...

Draining carbs after use is important if motor is used infrequently - petrol evaporates and oil is left to gunge up the carb internals. Stripping the carb and using an ultrasonic bath seems the best way of dealing with this - apart from not allowing it to happen of course...
 
Thanks TSB240. Great news that I can use copper wire to clean the fuel passage ways. The more I read the suggestions, the more I suspect the carbs and dried up fuel debris clogging the passage-ways. It would certainly explain why I have currently eight 2 stroke engines that don't work. There has got to be a common reason (either me or fuel). Also Sweden and the climate may be a factor. The water is always too cold to allow the engine to get hot despite the thermostat. Maybe. Lead free petrol and additives peculiar to local refineries.

FredRussel. Yes an International folkboat. It has always been my second boat for the past 30 years. 2.2 ton displacement. Still in production in Germany at a cost today of £50,000 bare. Choice of colours, Otherwise absolutely identical to satisfy class rules. No mainsail reefing points allowed, full sail to force seven. Any outboard spoils the line of the boat so, like fenders, I choose to unship the outboard and store in the lazerette when under sail. The extra weight of a 4-stroke and the storage probs would be a problem.

Thanks all. Copper wire and patience and I will let you know how many engines I can resuscitate in the next week or so. Snow blizzard and freezing temps at the moment means no testing after carb cleaning for a while.
 
The 2 stroke Malta I bought new ran fine for many years but with a bigger dinghy and daily use I was persuaded to uprate to a 4 stroke Suzuki which was totally unreliable, after 2 1/2 years I'd had enough of it. 1994 Tohatsu 2 stroke 9.8 bought very used was totally reliable for a few years until the thermostat clogged and it overheated. The new 2 stroke replacement has only had one season so far but also appears reliable.
 
Maybe something in my memory was trying to surface and it may be it has just happened. I recall that some years ago when I worked at Volvo, the side of the road was often littered with broke down cars in the winter. A few times I was one of them.

The problem was found to be the fuel pipe feed from the fuel tank at the back of the car that ran under the chassis to the engine at the front. Water in the fuel always sank to the lowest place which was that pipe which froze in the winter blocking the fuel. The car had to be towed to a heated garage or the car would be there till spring. It happened to me twice. After a few hours in the garage the car ran normally. Smart people poured an additive into the tank. Later I was told that the additive (a form of anti-freeze I suppose) was added by the fuel company. So I guess there is a different fuel recipe in cold countries. Not sure just guessing but additives may be part of the problem.
 
One thing I forgot to add is that I am very careful about getting my 100:1 fuel mix right.
A 35mm film container filled to brim with 2T oil is 30ml, that is mixed with three 1ltr milk bottles of unleaded.
I always give it a good shake before topping up the tank.
 
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My Tohatsu 18 2 st gets used every day and starts first pull every time. A set of new plugs every year and it gets 50 to 1 mix. It has been doing this for 5 years.

If you store a 2 st without running it dry expect problems when you try to put it back into service. Fuel with ethanol makes things worse. Even if you flush the tank fuel lines and carb thoroughly expect to have to clean the carb jets 2 or 4 times before ir runs reliably again.

As for 4 stroke small outboards they are spawned by satan and I would never trust one to get me home to my boat at night.
 
LadyInBed said:
One thing I forgot to add is that I am very careful about getting my 100:1 fuel mix right.
A 35mm film container filled to brim with 2T oil is 300ml, that is mixed with three 1ltr milk bottles of unleaded.
I always give it a good shake before topping up the tank.
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Can you check those figures - I don't believe a 35mm film pot is +/- 1/3 of a litre.
 
My three cylinder two stroke Suzuki GT380 was very nearly my nemesis. Over the four years I owned it, it blew pistons four times, and small end bearings endlessly. The only good I can say about it, is that it taught me everything I ever needed to know about motor vehicle mechanics. By the time I got rid of it, it had three different sized, (overbored) engine cylinders, though it did still go like stink.
 
There is a flow chart for 2 stroke engines it goes like this:

Start ---. Did you turn off the fuel and drain the carb when you put it away --yes/no

Yes: it will start next time

No: it wont start next time.

Good fresh fuel and a clean carb are the cure to 99.99% od two stroke "problems" ...
 
BurnitBlue said:
The water is always too cold to allow the engine to get hot despite the thermostat.
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Eh? Your engine should reach it's working temperature irrespective of the temperature of the water. Do you need to change your thermostat?

I've had some run-ins with smaller outboards over the years and the real problems have always been with the 4-strokes.

My current 80's vintage Suzuki 2.2 is great, totally reliable (so far) and destined to stay with me for many years. Maintenance priorities include fresh fuel with the correct 2-stroke oil mixed at the correct ratio and a new, correctly gapped spark plug fitted every year. Also, a quick squirt over the electrics with WD40 to keep the damp out. Always run it till it's hot and make sure it is worked reasonably hard. At the end of the run I always run it in the boatyard's fresh water tank to clean it out and also run it until all of the fuel is exhausted from the fuel system/carburettor. (I also carry a spare spark plug but have never needed to use it)

I also have a Yamaha 2 4-stroke which is the spawn of satan. It stays in my garage and I scowl every time I walk past it...
 
Ladybirdgaffcutter said:
If anyone has lots of gummed up jets, a small ultrasonic cleaner works wonders. Allendale brand reccommended. Works for cooker jets as well.
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Agree, if you keep having problems, there will be a workshop near you somewhere which will have one, also get the castings cleaned as well as the passages within can get blocked.
Cleaning fouled spark plugs.......just doesn't seem to work these days, I don't know if its something to do with the petrol, maybe the ethanol? I find if I have a duff plug that they soon stop working again when cleaned, so always replace them these days, after all it is normally only a few pounds.
 
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BurnitBlue said:
Thanks TSB240. Great news that I can use copper wire to clean the fuel passage ways. The more I read the suggestions, the more I suspect the carbs and dried up fuel debris clogging the passage-ways. It would certainly explain why I have currently eight 2 stroke engines that don't work. There has got to be a common reason (either me or fuel). Also Sweden and the climate may be a factor. The water is always too cold to allow the engine to get hot despite the thermostat. Maybe. Lead free petrol and additives peculiar to local refineries.
Snip

Thanks all. Copper wire and patience and I will let you know how many engines I can resuscitate in the next week or so. Snow blizzard and freezing temps at the moment means no testing after carb cleaning for a while.
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If it available to you I would recommend using Carb Cleaner, which is an aerosol spray of various aromatic solvents which are intended to dissolve the gums and varnishes inside the carburettors' delicate bits. In the UK it is best bought from motor factors rather than car accessory shops.
You still need to disassemble the carb to get at everything, but it is very satisfying to see the gunge dissolve and run off the parts leaving clean metal behind. Poking things into the jets might still be necessary but leaving the carb cleaner to soak means you don't need to poke so hard. A compressed air jet is also useful there, as are cocktail sticks to dig sludge out of corners.
My dinghy engine is a 1967 Seagull Featherweight and once woken up after the winter layup starts second pull for the rest of the season
Good luck
 
With the rise in ethanol content, I've found the use of a fuel stabiliser essential. No problems even with year old pre-mix.

I used to own one of those Honda 2hp four strokes. Dreadful bit of engineering; brute to start, with the centrifugal clutch, come alongside was a controlled crash, every nut and bolt tightened by a sumo wrestler, noisy as hell. Best bit was selling it to an unsuspecting Frenchman.
 
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Two things have always upset small two-strokes - old fuel-oil gumming up carb and long periods of low-speed running, which can oil up plugs. To that add modern fuel that seems to "go off" in storage. Didn't use to happen, I've taken a two-stroke out of my cellar and it started straight away on 5 year old fuel. Now I chuck last autumn's fuel and put in fresh stuff in spring.

Personally for dinghy tender engines I still like two-strokes for light weight. Carry a 2.5 two-stroke and 2.5 4-stroke for a couple of hundred yards and you'll know the difference.

On motorcycles there was one more thing that used to mess up two-strokes, long high-rev periods at very low throttle, ie going down very long steep hills - lack of oil could cause seizures.
 
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