2strokecalculator.com.au
| Ratio | mL per litre | % oil | Common use |
|---|---|---|---|
| 20:1 | 50.0 mL | 4.76% | Vintage / run-in |
| 25:1 | 40.0 mL | 3.85% | Older engines, break-in |
| 32:1 | 31.3 mL | 3.03% | Older dirt bikes |
| 40:1 | 25.0 mL | 2.44% | Older chainsaws, handheld tools |
| 50:1 | 20.0 mL | 1.96% | Modern Stihl, Husqvarna, Echo |
| 100:1 | 10.0 mL | 0.99% | Injection systems |
Running rich causes smoky exhaust, fouled plugs and carbon buildup. Won't seize the engine but kills performance and shortens plug life.
Far more dangerous. A lean mix starves the piston and crank. Seizure can happen within minutes. Always measure — never guess.
Check your owner's manual first.
Two stroke engines require oil mixed directly into the fuel because they don't have a separate oil sump like a four stroke engine. The oil lubricates the crankshaft bearings, connecting rod and piston as the fuel passes through the engine. Get the ratio wrong in either direction and you'll either foul the engine with carbon deposits or destroy it through lack of lubrication.
Always measure your oil using a proper measuring cylinder or a graduated mixing bottle — eyeballing it is how engines get wrecked. For a 50:1 mix you need exactly 20mL of oil for every litre of fuel. That's the equivalent of four level teaspoons.
Use a quality TC-W3 rated 2 stroke oil or one specifically labelled for air-cooled engines. Don't use automotive 4 stroke oil — it doesn't burn cleanly and will foul your engine. Common Australian brands include Penrite 2 Stroke, Castrol Power 1 Racing 2T, and Stihl HP Ultra.
Synthetic and semi-synthetic oils generally burn cleaner than mineral oils, producing less smoke and carbon buildup. They're worth the small extra cost for equipment you use regularly.
Two stroke engines are still widely used in Australia across a huge range of applications. Chainsaws, brushcutters, line trimmers, leaf blowers, concrete saws, outboard motors, dirt bikes, go-karts, model aircraft and jet skis all commonly run 2 stroke engines. Most modern handheld outdoor power equipment from brands like Stihl, Husqvarna, Echo, Makita and Ryobi runs at 50:1.
Older Australian dirt bikes — particularly Yamaha YZ and KTM models from the 90s and early 2000s — often ran at 32:1 or 40:1. Always check the manual for your specific model and year.
Premixed 2 stroke fuel degrades faster than straight petrol. The oil can start to separate and petrol loses volatility over time, especially with ethanol blends. As a general rule, use premix within 30 days for best results. If you're storing equipment for longer than that, either drain the tank and carburettor or use a fuel stabiliser like Sta-Bil.
Keep premix in a sealed, fuel-rated container away from heat and direct sunlight. Never store it in a clear container. Label it clearly with the date and ratio so you're not guessing later.
E10 (10% ethanol) is widely available at Australian service stations but it's not ideal for many 2 stroke engines, particularly older ones. Ethanol absorbs moisture from the air, which can lead to phase separation in stored fuel and corrosion in carburettors and fuel lines not designed for ethanol. If your equipment is more than 10 years old, stick to standard 91 or 95 octane unleaded where possible. Most modern equipment manufactured after 2010 handles E10 fine — check your manual.