Myths around 4 stokes

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dartmoor

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I was reading some old stuff on small outboards, and it seems to me that even before the demise of the small two stroke there were claims from manufacturers that 4 strokes were:

A) quieter than two strokes
B) more reliable
C) more durable
D) more fuel efficient

Strikes me that only d) is actually true? Is there any evidence on a-c - I think they are myths?
 
we have a new super quiet Mercury 9.9hp 4 stroke but yes the Honda 2 we had back in the UK was noisy on account of it having an air cooled cylinder head I believe. The Honda was super light on fuel as trying to run the carburetor dry took ages and ages and if you didn't the residual fuel would gum up the jets and make starting difficult if left any time or it would not run smoothly at low throttle without using some choke. WE used to add a little fuel stabilizer fluid to the fuel tank which helped during the season between infrequent outboard uses ( we rowed a lot and only used the motor for longer trips in the dinghy), but not if left for a longer time or over winter. I think the Honda 2hp was more prone to that than were other motors or larger Hondas.

I think the 4strokes have more thrust for the same hp, certainly our old Honda 2hp 4 stroke would plane our then Zodiac 285 fastroller dinghy two up which the Yamaha 2hp 2 stroke we had before that certainly would not
 
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dartmoor said:
I was reading some old stuff on small outboards, and it seems to me that even before the demise of the small two stroke there were claims from manufacturers that 4 strokes were:

A) quieter than two strokes
B) more reliable
C) more durable
D) more fuel efficient

Strikes me that only d) is actually true? Is there any evidence on a-c - I think they are myths?
Click to expand...

A) True. The pitch is usually lower and there are less power strokes per minute.

B) I have found them more reliable. If they won't start it is normally a genuine fault, rather than just being recalcitrant.

C) I haven't owned one long enough to compare durability, on a decade basis.

D) Certainly use a lot less fuel (and stink less)
 
charles_reed said:
an important G - 2-strokes have an infinitely higher power/weight ratio than 4 strokes. Important when age determines lifting power.
Click to expand...

Infinitely? So I can get 1000hp+ from my little Mariner. Or scale it down to a few grams? Please tell me how...;)
(But, yes, lightness helps.)

And don't forget 'S': invented by a Scot. Not like that humourless Teutonic rubbish.
 
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Norman_E said:
F is also correct. Fussier about which side you can lay them down in a locker.
G ?
H is also correct, Heavier!
Click to expand...

F) How many ways do you want to lay an engine down? Having taken it from the dinghy and brought it into the cockpit, how much of a struggle is it to make sure you put it in the locker one of (in most cases) two ways?

H) Depends on the model and spec. As you use less fuel, it is true there may be more fuel left in the integral tank. Different makes have differing variations in weight between the same power models. In some cases it is just a couple of Kgs.
 
I bought a new Japanese four stroke for my tender. Runs very smoothly, starts easily but stalls when you put it into gear. Not very helpful when you are leaving a lee shore to go out to the mooring. I have been told that in order to pass the emissions tests the mixture is too lean which causes it to stall. Don't know if this is true but have fixed my old seagull now!
 
Sensibly the original comparison by 4 stroke proponents did not include weight comparisons where the 2 stroke would win hands down.
 
Spot on, and with most outboard applications weight is crucial.

Even a strong fit bloke may struggle lifting an engine between cruiser & tender, and some smaller cruisers with an outboard on the transom are near crucified by heavy engines...
 
I have no experience of 4 stroke outboards but I have a mariner 3.3 and it's simplicity has to be a major selling point. It can serviced by a chimp with a set of mole grips
 
Why should a 4 stroke be more reliable than a 2 stroke ? What engineering basis is there for that hypothesis

Certainly, to date our 2 stroke, which was bought second hand on eBay, seems to have survived well on neglect (flush out in fresh water once every couple of years, new spark plug once every 5 years or so)
 
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