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Fuel Mixture Ratios
| Year Manufactured/ Notes* | Ratio | 1 gal. gas | 2 gal. gas | 5 gal. gas |
|---|---|---|---|---|
| 1931 to 1978 | 10:1 | 12.8 oz. oil | 25.6 oz. oil | 64 oz. oil |
| 1978 on (older converted models*) | 25:1 | 5.12 oz. oil | 10.24 oz. oil | 25.6 oz. oil |
| Roller bearing models ONLY** (25:1 recommended) | 50:1 | 2.56 oz. oil | 5.12 oz. oil | 12.8 oz. oil |
To calculate other fuel mix ratios, use CSGNetwork's online Marine Gas Oil Mixture Ratio Calculator.
Note: Outboards equipped with a Bing carburettor can use the 25:1 ratio.
*25.1 PETROL (GAS)/OIL RATIO
All motors manufactured from January 1978 are designed to operate on a 25:1 petrol (gas)/oil ratio.
Motors manufactured since 1967*** can satisfactorily use this ratio, providing the following modifications are made:
- FORTY FEATHERWEIGHT and FORTY PLUS MODELS - F & FP series fitted with the Seagull - Villiers carburetor. The No. 3 taper needle at present fitted should be replaced with a No. 2 needle (Part No. V654/2)... taper needle adjustment setting is standard... please see Service Sheet No. 7
- FORTY FEATHERWEIGHT and FORTY PLUS MODELS - GF & GFP series fitted with the Seagull - Bing carburetor. No modification required.
- SILVER CENTURY and SILVER CENTURY PLUS MODELS - WS & WSP series fitted with the Seagull - Amal carburetor. The No. 45 power jet should be replaced with the slightly smaller No. 40 jet (Part No. S7/062/40).
We recommend Seagull Two-Stroke oil, however, if this is unobtainable, use a good quality two-stroke oil.
**The 50:1 ratio is NOT RECOMMENDED for any British Seagull Outboard. If you know or don't know the model of your outboard, use 25:1 or better.
***Motors built prior to 1967 should retain the 10:1 petrol oil ratio.