What mixture?

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headdownarseup
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Re: What mixture?

Postby headdownarseup » Wed Sep 20, 2017 6:50 pm

.....which many are not by now, and need some careful nursing to keep 'em going.

OIL is only 1 very small part in all this.


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Keith.P
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Re: What mixture?

Postby Keith.P » Wed Sep 20, 2017 7:20 pm

I beg to differ, oil fuel mix is pretty much a critical factor when it comes to 2-strokes.
I have seen first hand on numerous occasions, what happens to motors run without oil or minimal oil, this normally equates to a totally destroyed engine in minutes, to reducing the life of an engine, I have even seen a piston with half it's skirt worn away, had minimal oil and a tight small end. Not talking about you Charles. :shock:

Oil maybe a small part, but more critical then people seem to think.

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Oyster 49
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Re: What mixture?

Postby Oyster 49 » Thu Sep 21, 2017 11:41 am

The original question:
I have a 1973 40+ which will be used as a "get me home" motor on a 13 foot Dory and as a "pottering about" motor on a small inflatable, presumably both uses will be mainly at full throttle.

So, should I keep it as a 10:1 original mix or replace the needle to allow a 25:1 mix?


And my initial reply:

A 1973 engine would have left the factory as 10:1 but it should be able to run at 25:1 quite happily. As a compromise I'd suggest going for a 16:1 mix on a standard needle and use the adjustment screw to weaken the mixture a tad to compensate for less oil (and thus more fuel) in the mix.

See how that goes, and of course you could go the whole hog and convert to a 25:1 needle.

headdownarseup
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Re: What mixture?

Postby headdownarseup » Thu Sep 21, 2017 6:24 pm

I'd still keep everything at 10:1 for something this old.
Tempting as it might be to convert to a leaner mix, these little engines are very outdated by today's modern designs. Whether the engine is being allowed to "potter" about at low revs or on the odd occasion at full throttle, i don't care what anybody says- oil is absolutely critical to something like this.
It's lasted this long without any intervention to its oil and fuel so why bother with it now.This is what i meant by "careful nursing" and not just find a good oil that doesn't smoke too much. There's much more to it than that.


I too have seen first hand what a 2stroke engine can do to itself in just a couple of minutes with the wrong oil content. I speak from personal experience having been sat on a particularly high revving 47cc water cooled minimoto at full chat during a warm-up lap and suddenly have the back wheel lock-up at near 60mph going into a corner. That little engine was reduced to an expensive pile of rubbish in seconds. It transpired my pit guy hadn't put any oil into the fuel at all.(twit :roll: ) Normally these little bikes would run somewhere at 25-40:1 depending on whether we were on an indoor or outdoor track. That cost me a lot of points in the championship that weekend, not to mention pound notes in the rebuild for the next race meet. :evil: Had it not been for that little escapade i could have (should have) finished 4th overall in my class, but it wasn't to be :cry:
Now you can see why i'm touchy about the subject of OIL in 2strokes.

So yeah, oil is pretty important for any 2stroke engine. Even more so in an old seagull outboard.



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Charles uk
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Re: What mixture?

Postby Charles uk » Thu Sep 21, 2017 9:01 pm

So that's a plus point for smokey fuel!
Make it idiot proof and someone will make a better idiot.

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Re: What mixture?

Postby headdownarseup » Fri Sep 22, 2017 7:16 pm

Absolutely. Thumbs up from me.
Oil is still much cheaper in the long run when you compare the cost against new (and sometimes obsolete) parts.
I still can't get to grips with why anybody would want to convert an older designed engine like a seagull to run on a leaner oil mix than what was originally intended by the manufacturer. I find this very difficult to understand why there are still plenty of people out there that think by cutting back on oil content that an already old (and perhaps knackered) engine will be able to cope any better with less oil. In the wrong hands it's only a matter of time before that little engine starts throwing its toys out of the pram. On the plus side however we've heard stories that previously converted gulls are still doing their thing happily it seems. I know which side of the fence i'm sitting on this subject.
It takes all sorts i suppose, and it keeps the forum busy with faq's and advice.

As you've seen there are differences between oils nowadays with more of a positive shift towards cleaner running, which for the most part has been taken care of by the oil manufacturer with endless laboratory testing etc.

Oil is IMPORTANT.
Take it from me


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NaughtyBits
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Re: What mixture?

Postby NaughtyBits » Fri Sep 22, 2017 7:40 pm

"I still can't get to grips with why anybody would want to convert an older designed engine like a seagull to run on a leaner oil mix than what was originally intended by the manufacturer."

Maybe a 10-12 page thread is in order, to expound upon the differences in the manufacturer's intentions and seagull engine design pre & post '78 (according to this same SOS site). :roll:

http://www.saving-old-seagulls.co.uk/faq2.html#fuelmix

"Can I run on less than 10 to 1?

Perhaps All motors after January 1978 left the factory with 25:1 conversions. Most models built after 1967 can be converted to 25:1. I have a stock of 25:1 needles for the Villiers conversions £6.00 plus postage. I also have conversion jets for the Amal 2 jet carbs, £6.50 plus postage.

Prior to 1968, engines had slightly different bearings and it is recommended to stay on 10:1, though I know of quite a few that have been running on 25:1 for years, with no apparent problems. However see further down the page for how to run on less oil without changing needle..."

Oyster's immediate reply was all the OP needed, imo.

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Oyster 49
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Re: What mixture?

Postby Oyster 49 » Sat Sep 23, 2017 12:17 am

Thank you naughty bits, I do try to talk common sense and avoid sprouting a load of tosh for the sake of it. The original point was as per Johns guidance on the SOS site. Perhaps I should have just linked that :roll:

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Collector Inspector
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Re: What mixture?

Postby Collector Inspector » Fri Sep 29, 2017 12:58 pm

Oyster 49 wrote:Thank you naughty bits, I do try to talk common sense and avoid sprouting a load of tosh for the sake of it. The original point was as per Johns guidance on the SOS site. Perhaps I should have just linked that :roll:


Pretty well much aye!

I love these discussions......how many years now between us?

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