2 Stroke Outboard Fuel Mix Ratio

50:1 100:1? Finding the right mix for your outboard.

two stroke outboard engine fuel mix guide

In this guide we step through the basics of how the right mix of fuel and oil for two stroke outboard engines.

Why mix Fuel & Oil anyway?

Any outboard described as a 'two stroke' engine is an internal combustion engine than burins injected fuel through a reduced power cyle of just ignition and exaust (more info about the difference between two stroke and four stroke engines here. ) Due to this design it is necessary to provide the engine with lubrication (the oil) actually within the injected fuel (the petrol or gas). The relative proportions of these two components is called the 'fuel mix ratio'.

Getting the mix right

Every engine will have it's own fuel mix ratio, often mandated by power, intended use and age of the outboard and manufacters state this required mix ration and any tolerance (if there is any!) in the owners manual.  Not running the right mix can cause poor starting, performance degradation, increase wear and tear and excessive smoke from the exhaust.



If however you don't have the original owners manual then you'll need to determine the right mix prior to use. Manufacturers often print the fuel mix ration on the inside or outside of the cowling, the fuel filler cap or sometimes embossed onto the fuel tank itself.

Yamaha two-stroke fuel mix ratio
This Yamaha's fuel mix ratio is clearly marked on the cowling

If all else fails a quick internet search of your outboard make, model and age will quickly reveal the required ratio.  If you're absolutely stuck we recommend a mix of 50:1 for outboards older than 1980 and 100:1 for outboards manufactured since 1980. That is 50 parts fuel to 1 part oil and 100 parts fuel to 1 part oil respectively.

Mixing the Fuel

Once you've landed on the ratio you need actually do the mixing.

Always store, handle and mix outboard engine fuel in a well ventilated space, ideally outdoors and away from any source of ignition of chance of contamination, i.e. not on the ground of some dusty car park!

Prepare you fuel, oil on a bench or other suitable surface and have a clean rag and medium sized funnel handy. Aim to add the oil to the fuel rather than the other way around so have a suitable rounded number volume of fuel ready in a container (Starting with 5 Litres of petrol in a tank is ideal) and then added you two-stroke oil through the funnel mixing thoroughly.

Once you've finished mixing clean-up an spilt fuel or oil and make sure to commit to memory or note down which fuel tank has the mixed fuel ready to go.

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