4 stroke or 2 stroke outboards

[Seajet]

How's that then ?

Oil in the petrol, both run out at the same time, both start again the same time next time.

I seem to have got away with it for 40 years...

 

[Skylark]

Does your engine increase speed as it runs out of fuel? The mixture is weakening very significantly. It's under no load so it will increase speed with a reduced a/f ratio. It's also running at high speed with very little lubrication, hence more likelihood of wear.

 

[TSB240]

Just to state the obvious, with an apology to all egg sucking grandmothers, it's not wise to run a 2t out of fuel as you will be leaving it without lubrication. Outboards usually have a fairly accessable drain plug to empty the carb.

David apology accepted this grandaddy never had a problem in 35 years.

Its much too messy to do what you suggest at the end of a long day.

I suspect it was also an old wives tale put out by the ob service guys. Ensures that they get plenty of gummy carbs to clean

 

[Seajet]

Does your engine increase speed as it runs out of fuel? The mixture is weakening very significantly. It's under no load so it will increase speed with a reduced a/f ratio. It's also running at high speed with very little lubrication, hence more likelihood of wear.

David,

neither the 2 or 5hp's speed up; the mixture stays the same, just the fuel runs out; it's either getting oil & petrol & running, or it's not.

The 2hp has no clutch so will be under load until it stops, the 5 doesn't speed up whether in gear or neutral; and starts again very easily, even without priming via the squeeze bulb.

 

[macd]

Does your engine increase speed as it runs out of fuel? The mixture is weakening very significantly. It's under no load so it will increase speed with a reduced a/f ratio. It's also running at high speed with very little lubrication, hence more likelihood of wear.

Yes is does increase speed, as you'd expect, for the reason you state.
Why do you state it's under no load: it might be, it might not. And if it weren't under load, why would it be running at "high speed"? It'd just speed up a bit. The bigger risk with a leaned-out mixture isn't lubrication loss but higher combustion temperatures and resulting detonation.

This might be a factor if you were hammering down the back straight at the old Snetterton on a TZ350; it was certainly a factor up to the 60s when you shut the throttle at the end of a long straight: Bultacos, in particular, were notorious for nipping up under such circumstances.

But a tender outboard is in such a low state of tune that the risk doesn't exist. (Check the plug's heat rating, typically around 6; a highly-tuned stroker would be at 10 or more.) (Readers planning to go classic bike racing on highly-tuned Seagulls should not necessarily take comfort from this.)

Incidentally, road bikes used to run out of fuel from time to time. They all went on to reserve fairly regularly, which amounted to the same thing. Ever heard of one seizing in the process? In theory it could happen and I daresay that very, very rarely it did, but I never heard of it.

 

[TSB240]

Does your engine increase speed as it runs out of fuel? The mixture is weakening very significantly. It's under no load so it will increase speed with a reduced a/f ratio. It's also running at high speed with very little lubrication, hence more likelihood of wear.

Best technique turn the tap off as you are motoring back to shore...Engine is cooled and lubricated under load at max revs until it cuts ... No problem

If you cut the fuel too late choke it to minimise increase in no load revs and provide a supply of petrol and oil into the crank case to give everything a nice coating of oil.

Used to race 2T air cooled kart engines you could guarantee a very fastlap with the high jet screwed in half a turn.

Give you up to 18,000 rpm for about 2 minutes before the little end overheated and you ended up with a bag of bits to take to scrutineering

Choke on overrun into corners was also used to dump fuel into engine to avoid overheating and seizing.

Now if you cut the fuel too early

 

[Lakesailor]

Two strokes don't rely on pressure fed oil to maintain a lubrication film between bearing surfaces.
The petroil mixture merely provides a film of lubrication to the roller bearings.
Running for a short while without a supply of oil mist is no problem at all.
The lack of lubrication on the cylinder walls is slightly more of a problem except you aren't gunning it under load so temperatures won't be significant.


Pro 2 stroke arguments revolve mainly (it seems) around the weight issue. So 2 stroke fans would seem to mainly using the motors on tenders.

 

[CreakyDecks]

I think a good case can be made for banning two strokes in fresh water. They do cause more pollution, partly because of the oil but more because they don't burn their fuel very efficiently. I see no problem with them on the sea. As others have said, the only time they have given me a problem is when running at minimum revs for a long time. I used to use my little two cylinder Johnson, rather than my single cylinder Yamaha, when pike fishing for this reason. At least I'd have one working cylinder when the lower one oiled up! I don't think this could be classed as "unreliability" because it was completely predictable. I'd troll around the lake or loch for a couple of hours, the lower plug would oil up and I'd go ashore so the dog could go and stretch his legs while I changed the plugs. It wasn't worth buying a four stroke, because I'd still have to go ashore for the dog anyway!
Incidentally, that Johnson doesn't have a separate fuel tank, so it has run out of fuel hundreds of times with no apparent damage. Why would it cause a problem? The fuel runs out - it stops!

 

[onesea]

4 stroke or 2 stroke think I would agree 2 stroke for a tender without question.

For a main engine? Run at high revs long periods working hard my thinking is 2 stroke is better. Trolling around 4 stroke is better...

.....at the end of the season I try to run down stocks of fuel, any left when the boat is ashore goes into the car or lawnmowers, always fresh fuel for the new season.

I was told, don't know if it's true but seems good practice to follow, that modern unleaded petrol goes to gummy jelly a lot quicker than the good old stuff, 3 months is pushing it.

With that & regularly flushing the engines in fresh water ( inc taking the head off the Mariner 5 which has a bit of a tendency to salt up ) I don't get problems, touchwood....

When it comes to storage this is a nightmare the only thing I buy petrol for is the outboards, both cars are diesel. Trying to run fuel down and keep enough onboard is a nightmare. Before now I have offered to give it away, when I explain why it has been refused.

I now use fuel stabiliser and normally manage to keep the engines running easily. I recon I get 4-6 months shelf life, if it starts running rough I drop 5 lts of fresh in to 10 or so liters of old.

As for keeping engines I now treat my 2 and 4 stroke the same, if I am going to use them in the next week or so I leave the fuel in the carb. If I am not going sailing in a week or so I will run it dry preferably in fresh water, not salt.

After a long whilst struggling to find a balance, this works for me but it takes some management keeping fuel fresh.

 

[JClarkes]

If using my Mariner 2hp 2 stroke on the tender, I always shut off the fuel before reaching the slipway, so that it doesn't spill fuel when I tilt it.

The fun of judging when to shut of the fuel. Sometimes you over do the stop, sometimes you under judge the timing resulting in a poke or two from the oar but dont you just love it when you judge perfectly and engine dies and you just touch your destination....

 

[jordanbasset]

Perhaps I have been lucky but on the 30 months I have been using a Yam 4 stroke 4hp engine (second hand when we got it) I have never had problems with 'stale' petrol or any other problems. In the summer months, since we arrived in Greece, we may only need to use the outboard every 2-3 weeks, rest of the time we are close enough to use oars or tied to the quay. When we do use it, it starts on the second or third pull without any problems. After winter it does take half a dozen pulls or so to get it going but fine after that.

 

[duncan99210]

I've had a series of small 2 stroke outboards over the years. Never gave any of them much in the way of tlc. Didn't worry about the fuel in the carb except at the end of the season, when it was drained. Didn't try and run the engine dry before putting it away for the week - never could remember to trun the fuel off before reaching the jetty. Never had any problems with any of them - changed the plug at the start of the season if it was difficult to start and the gear oil if it felt about time to do it - and that was it. Wouldn't have 4 stroke if you gave me one, as the current 2 stroke is quite heavy enough!

 

[Lakesailor]

Wouldn't have 4 stroke if you gave me one, as the current 2 stroke is quite heavy enough!

Yamaha 2 stroke 4hp 21Kgs


Yamaha 4 stroke 4hp 22Kgs

 

[CAPTAIN FANTASTIC]

I suspect this thread is a bit of a wind up. However it all adds to the fun of fair, so:

I had one of the ubiquitous Tohatsu style, 2 stroke, motors from new. It was immersed in seawater three times, once for the whole afternoon boozer opening hours. I had it for 15 years, it was frugal with fuel, powerful, never failed to start, never needed a spart part and was running like a new un when I sold it.

I bought a new 3.5 in advance of the ban. I have no plans to buy a four stroke, unless it's a motorbike.

It is not a wind up; I sincerely can not see any substantial benefits of having 2 stroke engines; apart from being able to lay them down either side; is this such a major advantage?

I enjoy the reliability of the 4 stroke and the ability to start them almost on the first pull and idle until ready to go; no need to mix oil; by far more economical; usually higher torque; and weight is almost the same nowadays.

 

[Bosun Higgs]

reliability being the major reason.

did you use a Seagull? My old Mariner was 100% reliable.

 

[macd]

usually higher torque

Don't think so

 

[CAPTAIN FANTASTIC]

did you use a Seagull? My old Mariner was 100% reliable.

Over the last 40 years, I have used many 2 stroke outboard mainly because that is all we had those days.

However, in the last ten years or so, the 4 strokes have progressed enormously, and in my opinion, the 4 strokes have overtaken the 2 strokes in almost every way.

I do appreciate that there are people out there with 2 stroke engines who had them for a long time and they are happy to carry on using them; however, it is surprising to hear of people who are prepared to pay good money for an old 2 stroke, without realizing the benefits of a modern 4 stroke engine.

 

[Laurie]

Tis interesting this......

The day of the 2 stroke internal combustion engine is yet far from dead, legislators permitting, & there is much developmental work on going, especially with motorcycle engines.
They are lighter, simpler, more efficient, but emit a higher unburnt hydrocarbon output per revolution (less of some other toxins/carcinogens, though), most of which is all to the good, especially in conservation terms. 4 strokes, having more components, inherently have a far greater energy & pollution input in their construction, to say nothing of higher frictional losses.....

With respect to consumption & unburnt hydrocarbon emissions, Hooper & Favill (I think?) developed in the 70s a series of "stepped" 2 stroke motorcycle engines of 350, 500, & 750cc twins, where one cylinder scavenged the exhaust of the other, & thereby ran a lot more "cleaner". It showed a lot of promise under the Norton "Wulf" banner. What happened is well documented & oft repeated history.
I'm no engineer, but I reckon the 2 stroke is not yet done, & yes my tender is powered by a 8 hp Tohatsu 2 stroke, at around 22kg. Is there an 8hp 4 stroke at that weight........? I'd love to know?

ps the idea of 4 strokes generally having a higher level of (peak) torque is often as not a fallacy. Historically, however, 4 strokes have been able to offer a wider spread of torque. Not quite the same thing....
However to jump back to the motorcycle theme, a large capacity 4 stroke Italian V twin is a joy to behold.....!!

 

[grumpygit]

I suspect this thread is a bit of a wind up. However it all adds to the fun of fair, so:

I had one of the ubiquitous Tohatsu style, 2 stroke, motors from new. It was immersed in seawater three times, once for the whole afternoon boozer opening hours. I had it for 15 years, it was frugal with fuel, powerful, never failed to start, never needed a spart part and was running like a new un when I sold it.

I bought a new 3.5 in advance of the ban. I have no plans to buy a four stroke, unless it's a motorbike.

+1 . . . . .We have a Mercury 2.5 and a Tohatsu 3.5, both 2 strokes, absolutely no problems at all.

Many a time they have towed temperamental 4 stroke powered tenders back to their mother ship.

4 strokes require oars and muscle. . . . . . . . .

____________________________________________________________________

 

[macd]

With respect to consumption & unburnt hydrocarbon emissions, Hooper & Favill (I think?) developed in the 70s a series of "stepped" 2 stroke motorcycle engines of 350, 500, & 750cc twins, where one cylinder scavenged the exhaust of the other, & thereby ran a lot more "cleaner". It showed a lot of promise under the Norton "Wulf" banner. What happened is well documented & oft repeated history.
I'm no engineer, but I reckon the 2 stroke is not yet done, & yes my tender is powered by a 8 hp Tohatsu 2 stroke, at around 22kg. Is there an 8hp 4 stroke at that weight........? I'd love to know?

ps the idea of 4 strokes generally having a higher level of (peak) torque is often as not a fallacy. Historically, however, 4 strokes have been able to offer a wider spread of torque. Not quite the same thing....
However to jump back to the motorcycle theme, a large capacity 4 stroke Italian V twin is a joy to behold.....!!

The future of 2-strokes is widely regarded as direct injection (fuel not introduced until exhaust port closes, so no chance of unburnt fuel vanishing down the pipe). It is of course now a reality, but too expensive for smaller/cheaper engines. Whether it can make strokers common again is debateable: countless $millions have been spent on it by Ford, GM, Mercedes and others, and we've still yet to see a production 2-stroke car so equipped.

re your PS: yes to all.