How to Mix 2 Stroke Fuel for Petrol RC Cars

A 25:1 fuel mix is 40 ml of 2-stroke oil for every 1 litre of unleaded petrol. That is the standard ratio for large-scale petrol RC cars, and it is the ratio the Rovan Bajas we sell ask for. For 2 litres use 80 ml, and for 5 litres use 200 ml. If your engine's manual gives a different ratio, follow the manual.

25:1 means 25 parts petrol to 1 part oil. Note the last row: 5 litres of petrol plus its oil will not fit in a 5 litre can.

What you need to mix 2-stroke fuel

• Unleaded petrol from a petrol station.

• 2-stroke oil. Not the cheap stuff you'd put in a lawnmower. Buy a fully synthetic oil made for high-performance 2-stroke engines.

• A clean container made for fuel. Not an old milk bottle. A Rovan 1L ratio mixing bottle has the ratios marked on the side, which takes out the guesswork. For bigger batches and for storage, use a proper can such as the Rovan 5L jerry can.

How to mix 2-stroke fuel, step by step

Step 1: Set up outside

Mix fuel in a well-ventilated place, away from anything that could light it. Outside is best. Wear safety glasses and keep it off your skin. Make sure the bottle or can is free of dust and dirt: dirty fuel damages engines.

Step 2: Measure the petrol

With a ratio mixing bottle, fill the main chamber with unleaded to the fill line you want, for example the "1" mark for one litre. With a plain jerry can, use a measuring jug and pour in exactly 1 litre.

Step 3: Measure and add the oil

With a mixing bottle, fill the separate oil chamber to the matching "1" mark on the 25:1 scale. By hand, measure exactly 40 ml of oil and pour it into the petrol. Don't guess: eyeballing the oil is a recipe for a seized engine or a fouled spark plug. A marker line on the bottle's 25:1 scale makes it easier to see in poor light.

Step 4: Mix

Seal the container. With a mixing bottle, tip it so the two chambers combine. Then shake the bottle or can for about 30 seconds so the oil and petrol blend completely.

Step 5: Store it properly

Don't keep fuel in the mixing bottle. Pour it into a sealed jerry can. Mixed fuel goes stale, so mix small batches and don't run old fuel.

After the run: drain the tank

Always drain the fuel tank after a session. Mixed fuel left sitting in the tank goes stale and can gum up the carburettor. If that has already happened, see how to reset a carburettor to factory settings. Replacement fuel tanks and tubing are here if yours has perished.

New car? The Baja 5B quick start guide covers the first start, and electric, nitro or petrol explains how petrol engines differ from nitro.