Oil mix ratio for 4hp 2 stroke outboard

[sailorman]

I remember seeing somewhere that the Yamaha warranty for commercial and retial was different... In commerial use they required 50:1 to honour the warranty, in leisure 100:1

Yams & most small O/bs are made by Tohatsu & re-badged.
Tohatsu own brand use 50/1

 

[VicS]

I run at 100:1 because not only does it run well but moving the decimalplace 2 places to the left is easy.Incidentally in 1980 leaded petrol was the norm so I add a little additive when I fill my decanting 5 litre can. Anybody else use a leaded petrol additive. My 30 year old outboard is still running well...

Making the arithmetic easy is no justification for using a 100:1 mix ( In the US they manage to work out fuel mixes in ounces and gallons .. not yet having discovered litres and millilitres .. they do struggle at bit at times though )

If the engine was originally sold as a 100:1 mix engine, is used lightly, and not run at WOT for long periods then 100:1 is Ok but be sure to fog it out before storage because 100:1 does not leave enough residual oil to protect the internals. I believe that engines seizing up during storage was one of the reasons OMC discontinued with 100:1 as a fuel mix after only a 2 or 3 year period in the 1980s.

The lead or lead substitute is only required for lubricating valves or increasing the octane rating for high compression 4 strokes.

There is no reason to use any such additive in a two stroke.

 

[Fire99]

My Mariner 2.5 (2001 model) is recommended to run 100:1

Ran for 9 years at 100:1 and a brief fling at 50:1 this year.

It smells nicer at 50:1 with that notable 2-stroke smell and you get a little bit of smoke on start. Does run better on 100:1 so that's where I'll stay with my engine.

 

[jwilson]

I run at 100:1 because not only does it run well but moving the decimalplace 2 places to the left is easy.Incidentally in 1980 leaded petrol was the norm so I add a little additive when I fill my decanting 5 litre can. Anybody else use a leaded petrol additive. My 30 year old outboard is still running well...

I have been told by engineers that two-strokes are most happy on low-octane fuel. Also that leaded petrol in two-strokes encourages spark plug whiskering, though it used to be difficult to get anything but leaded.

 

[ghostlymoron]

[ QUOTE ]
the manufacturer would be Tohatsu as the make most small o/b engines that are then re-badged.
the reseller tells you what you want to hear, no more oily engines so 100/1. want long life use 50/1 /forums/images/graemlins/tongue.gif

[/ QUOTE ]

Just a PS......Long life?? 20 years and still going strong not good enough for ya then?

20years is nothing. My Seagull has been running for 45 years and still going. 20:1 mix though.

 

[VicS]

20years is nothing. My Seagull has been running for 45 years and still going. 20:1 mix though.

Until 1978 and with the exception of a few very old models Seagulls normally ran on 10:1 mix. From 78 onwards they ran on 25:1 A few very late models were sold to run on 50:1 but very of those are thought to have survived the experience! Models produced after 1967 can be converted to run on 25:1 Villiers carbs need a different needle, Amal carbs need different jets ( Bing carbs need no modification). Without modification they can usually be adjusted to run on 16:1 and sometimes 20:1.

It is not generally advised to run earlier models on 25:1, because the bearings were different, although many do.