Running a 2-stroke outboard dry before storing ?

VicS said:
Who cares ?

Does the composition of Avgas or whether it float,s or not, have any relevance as to whether, or not, to run a small outboard dry before storing
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Yes. If the fuel has water in it then when it eventually evaporates in the tank/fuel lines/carburettor then the moisture may remain and cause corrosion. It it remains separate then any water in the fuel will firstly stop you from starting the engine (the pick up is usually at the bottom of the tank where the water is), so in order to run the engine dry you need clean uncontaminated fuel in the first place......which you then run through the system and drain out by running it dry....
 
For what its worth, i always used to "over oil" slightly my last 2 stroke mix before lay up. Guaranteed to get oil where you want it. Simple and easy!!
Triassic said:
Yes. If the fuel has water in it then when it eventually evaporates in the tank/fuel lines/carburettor then the moisture may remain and cause corrosion. It it remains separate then any water in the fuel will firstly stop you from starting the engine (the pick up is usually at the bottom of the tank where the water is), so in order to run the engine dry you need clean uncontaminated fuel in the first place......which you then run through the system and drain out by running it dry....
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RichardS said:
That's going to be a tricky one. The colloquial opposite of "to emulsify" is "to separate" and that's the opposite of what you mean I believe. :D

Richard
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An emulsion is quite distinct from a solution, at least in my view.
An emulsion is small (going on microscopic) globules of fluid A suspended in fluid B.
A solution is molecules (or even atoms/ions) of substance A dissolved in fluid B.

An emulsion will often separate out, a solution will generally not unless you evaporate the solvent or change the temperature etc.
A classic emulsion is like salad dressing where two clear fluids mix to make a cloudy mixture. It's cloudy because there are lots of little pockets of the two fluids with loads of boundaries between them.
Leave it alone and it will separate, whereas gin won't separate into alcohol and water.
 
lw395 said:
No, it's the opposite of that. The ethanol supposedly acts as a co-solvent and dissolve the water in the fuel. I suspect the flip side of this is if it's already got saturated and is bringing water into the carb.
AIUI, people used to put alcohols, usually methanol, into petrol for this purpose?
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Dunno about all "people" but methanol was used in competition engines because, for a variety of reasons, it allowed higher compression ratios and gave more power. The main penalty was huge fuel consumption: often you'd just chuck away the main jet and let the engine guzzle as much as it could. In Manx Nortons (which were bad enough on petrol but miles worse on methanol), it also tended to vibrate out your fillings, as I learned to my cost :ambivalence:
 
NormanS said:
I have always run my outboards dry. If you leave "petroil" in the carburettor for any time, the petrol will evaporate, so the next time you try to start, the mix will have too much oil in it, and it may be more difficult to start.
It doesn't really mean running the engine without any lubrication. It's only on tick-over, and will stop as soon as there's no petrol ( and oil) left.
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I was having a lot of problems in Greece with a 2hp suzuki (4 stroke). The slow running jets were constantly gumming up and there was always a crystalline gunge in the float chamber. I always used to run the motor dry every time I used it.

An engineer in Greece suggested that was the problem and that instead of running dry, you should drain the float chamber. I now do this, and have had no more problems. He explained that when you run it dry of fuel the fuel coming through the slow running jet evaporates each time leaving a further layer of gum. So rather than helping, it may be the cause.
 
macd said:
Dunno about all "people" but methanol was used in competition engines because, for a variety of reasons, it allowed higher compression ratios and gave more power. The main penalty was huge fuel consumption: often you'd just chuck away the main jet and let the engine guzzle as much as it could. In Manx Nortons (which were bad enough on petrol but miles worse on methanol), it also tended to vibrate out your fillings, as I learned to my cost :ambivalence:
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but that is just part of the problem.

petrol with methanol, ideally needs a larger jet. Without, the mixture must be leaner, hence all the difficulty starting and poor running while warming up.
 
david_bagshaw said:
but that is just part of the problem.

petrol with methanol, ideally needs a larger jet. Without, the mixture must be leaner, hence all the difficulty starting and poor running while warming up.
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Of course. But the price was worth paying with competition engines (in the relatively few places and disciplines where methanol was permitted). It certainly wasn't in civvy street.
 
NormanS said:
As I have said already, I always run my little outboard dry. If you are running onto a beach, the engine is going to be tipped up anyway, so fuel left in the float chamber is going to be spilled out, so I try to judge when to switch off the fuel.
Not only am I getting the use of all the fuel, but also saving the world from all that needless pollution.:D
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The fuel in your float chamber should remain there when the engine is tilted up. If it spills out I would suggest that something is seriously wrong.
 
lw395 said:
An emulsion is quite distinct from a solution, at least in my view.
An emulsion is small (going on microscopic) globules of fluid A suspended in fluid B.
A solution is molecules (or even atoms/ions) of substance A dissolved in fluid B.

An emulsion will often separate out, a solution will generally not unless you evaporate the solvent or change the temperature etc.
A classic emulsion is like salad dressing where two clear fluids mix to make a cloudy mixture. It's cloudy because there are lots of little pockets of the two fluids with loads of boundaries between them.
Leave it alone and it will separate, whereas gin won't separate into alcohol and water.
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Wow ... you're taking this very seriously despite all my smiley efforts. :)

A micro-emulsion operates on a microscopic level, can be transparent, and can be permanently stable and this may well be the mechanism you are describing.

But whatever, it might be simpler just to agree with me that "to emulsify" is the coloquial opposite of "to separate" and therefore the opposite of "to emulsify" is definitely not how you would wish to describe the dissolution of water in petrol. :encouragement:

Richard
 
Spirit of Glenans said:
The fuel in your float chamber should remain there when the engine is tilted up. If it spills out I would suggest that something is seriously wrong.
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ITYWF that Seagull outboards have a little overflow hole, out of which fuel gushes when you "tickle" the carburettor, and also when the outboard is tipped up, so nothing "seriously wrong" at all. Not sure about slightly more modern outboards, but old habits die hard.
 
macd said:
Dunno about all "people" but methanol was used in competition engines because, for a variety of reasons, it allowed higher compression ratios and gave more power. The main penalty was huge fuel consumption: often you'd just chuck away the main jet and let the engine guzzle as much as it could. In Manx Nortons (which were bad enough on petrol but miles worse on methanol), it also tended to vibrate out your fillings, as I learned to my cost :ambivalence:
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Totally different conversation from a few % alcohol in petrol.
 
david_bagshaw said:
...
petrol with methanol, ideally needs a larger jet. Without, the mixture must be leaner, hence all the difficulty starting and poor running while warming up.
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No that's entirely false, pump petrol containing ethanol has at least the same calorific value as olde worlde unleaded, to much better accuracy than a carburettor works.
 
lw395 said:
No that's entirely false, pump petrol containing ethanol has at least the same calorific value as olde worlde unleaded, to much better accuracy than a carburettor works.
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not sure where cal value comes into it but methanol , which is what david bagshaw was talking about , needs a very different fuel/ air ratio to what gasoline requires.

You will see this if you use these equations

for methanol

2CH3OH + 3O2 --> 2CO2 + 4H2O​

and taking 2,2,4-trimethylpentane as the average formula for gasoline

2C8H18 = 25O2 --> 16CO2 + 18H20​

and take the density of methanol as 792 kg m-3, that of trimethylpentane as 690 kg m-3 and air to be 21% oxygen

to work out theoretical fuel to air volume ratios

Do the same for ethanol!
 
Or in terms we can all understand...... and my thanks to the TR Register from whom I pinched it.


The ideal fuel/air ratio for a petrol engine (Stoichiometric Air/Fuel Ratio) is between 14.5 & 14.7 to 1. That is 14.7 parts air to 1 part fuel by volume. For pure Ethanol this ratio is between 8.9 & 9 to 1. (9 parts air to 1 part fuel).

This can partly be explained because Ethanol contains 35% Oxygen by weight and therefore will naturally ‘lean-off’ the fuel/air mixture.

Even at only 5% mixture, Ethanol will alter the correct fuel/air ratio and lead to unadjusted engines running weak. (As a very crude guide…slightly rich mixtures will result in wasting fuel. Slightly lean mixtures can result in significantly increased combustion temperatures.) To further add to the problem, vaporisation can lead to incorrect fuel metering and a further ‘leaning’ effect (Enleanment). It should be noted that an increase in combustion temperatures will not necessarily register on the vehicle’s temperature gauge. This gauge predominantly operates via a sensor in the cooling system (usually in the cylinder head) and records the temperature of the coolant directly in contact with the sensor. This is usually accurate enough to indicate if the engine is operating within its design temperatures. Permanent damage may already have occurred to valves and pistons before any change is noticed in coolant temperature.

There's loads more in the article if you're still awake....
 
Yes, and beware of squirting snake oil down carbs as our local "Marine Engineer " (said in the loosest possible terms). While performing the said proceedure in the flush tank at the local sailing club in an attempt to impress bystanders managed to provide an unusual noise and immediate cessation of rotation. Result bent connecting rod!!
 
Triassic said:
Or in terms we can all understand...... and my thanks to the TR Register from whom I pinched it.


The ideal fuel/air ratio for a petrol engine (Stoichiometric Air/Fuel Ratio) is between 14.5 & 14.7 to 1. That is 14.7 parts air to 1 part fuel by volume. For pure Ethanol this ratio is between 8.9 & 9 to 1. (9 parts air to 1 part fuel).

This can partly be explained because Ethanol contains 35% Oxygen by weight and therefore will naturally ‘lean-off’ the fuel/air mixture.

Even at only 5% mixture, Ethanol will alter the correct fuel/air ratio and lead to unadjusted engines running weak....
There's loads more in the article if you're still awake....
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This is spaffed all over the web by classic car and bike people.
There is little to no truth in it.
E10 fuel typically requires more air not less.
From BP:
http://www.bp.com/content/dam/bp-country/en_au/media/fuel-news/fuel-octane-power.pdf
 
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