2 stroke oil 4 stroke outboard...

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Andrew_Trayfoot

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A local marine mechanic advised me to add a small amount of 2 stroke oil to the petrol of my Yamaha f2.5 to help keep the carb clean.

I have used small amounts of 2 stroke, premixed for my hedge trimmer, in my Honda 4 stroke lawn mower with no problems in the past. In fact the lawn mower is far more reliable than than the outboard and gets far worse treatment....

Any views?
 
Agree, I cant see it being of any benefit to be honest. I know what you mean about these little outboards though. My 6hp Merc is a pain in the arse compared to my old honda lawnmower that never gets serviced and works on the third pull every time!!!!
 
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I wouldnt take much notice of your mechanic. 2 stroke oil will not keep your csrb clean, will lessen the life of your fuel, can cause your plug to break down and most importantly can cause valve seat regression. Keep your fuel fresh . Adding a little fuel stabiliser will be more beneficial tha adding oil
 
snowbird30ds said:
Outboard will probably run hotter as carb jets are sized for petrol not petrol/oil mix, the volume taken by the oil will make the fuel mixture leaner hence running hotter.
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That's complete nonsense.

Personally for a 4 stroke, I would just try to use petrol that is as new as possible and always stored in an unvented container.
I have heard that some small carbs have corrosion issues that are improved by a small amount of 2T oil. Apparently some industrial users of things like lawnmower engines find something like 200:1 works well. But others find no difference.

I find with motorbikes that using a premium petrol like BP's more expensive version seems to help clean the system of a machine that's not been used for a while. but mostly what these things want is to be used regularly.

Really we shouldn't be taking small outboards to a mechanic, we need to be able to clean out the carb ourselves. I do my little Yamaha more than once a season. One day, being able to clean your own carb will save you a long row!
 
Many years ago when looking at a perspective boat purchase, the owner assured me he had always followed the instructions re the petrol/oil fuel mix. This puzzled me since the engine was a two cylinder Albin (Volvo) petrol four stroke. Looking further I noticed the boat had been fitted with a Stuart Turner fuel tank complete with mixing instructions for fuel mix on the filler cap. He had, for years, religiously followed its instruction !
 
RichardS said:
I wish someone had told me that 50 years ago when I was tuning two stroke engines. ;)

This guy has swallowed the myth hook, line and sinker: http://www.off-road.com/dirtbike/tech/twostroke-fuel-ratios-premix-myth-vs-reality-54169.html

Richard
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Possibly if you are talking about primitive mineral oil at 16:1 instead of 20:1, it will be a significant loss of petrol. but it's still only the difference between 94% petrol and 95% petrol.
The smallest change you can make in an Amal main jet is 2%.
Maybe changing from 50:1 synthetic to 16:1 castor oil could catch you out, but chances are other changes will have been made which are more likely to be the real cause. Favourites being removing/modifying exhaust baffles and air cleaners?

The article is also a bit dubious about ring sealing. Ring sealing is necessary for an engine to start, but at 10,000 rpm, the rings don't need to work nearly as well. There isn't time for much gas to flow through a small gap!. Lots of racing engines have less rings than road engines. High revving model aircraft engines don't always have them at all. Too many rings= too much friction. OTOH, race engine rings are not expected to last very long.

Fair point, oil mixes less than 20:1, the viscosity will be making a difference. I can't see a ratio like 50:1 being significantly more viscous than straight fuel though?
 
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