Kart Fuel Mix: The Right Petrol, Oil and Ratios for Rotax Engines
In a two-stroke the mix is not just fuel: it is also all the lubrication the engine receives. Getting it wrong does not mean going slowly: it means putting the engine at risk. Here are the right ratios for the Rotax, which petrol to use, which oil and how to prepare the can without mistakes.
In short On the Rotax you use a 2% mix in normal running and 3% during running in, with 95 to 98 octane petrol, always fresh. The 2% is calculated on the total mix: for 10 litres of petrol the exact figure is 204 ml of oil, not 200. In Rotax races XPS Castor Racing Oil 2T is mandatory.
The ratios: 2% in normal use, 3% for running in
For the Rotax MAX the reference ratio is 2% oil (1:50) for normal use and 3% during running in, for the first 10 litres of petrol. Recommended oil: XPS, developed together with Rotax. In Rotax MAX Challenge races XPS Castor Racing Oil 2T at 2% is mandatory.
Translated into the can, the quick Rotax table says 20 ml of oil per litre of petrol: 100 ml for 5 litres, 200 ml for 10. During running in you use 3% for the first 10 litres of petrol: 0.3 litres of oil per 10 litres, i.e. 30 ml per litre. Always with a graduated measuring cup, never by eye. But if you want a perfect 2% or 3% there is a detail that almost nobody explains, and it deserves a chapter of its own.
2% of what? The detail almost nobody explains
Stop for a moment on this question: 2% of WHAT? When people say "2% mix" they mean that in the finished can (the one you will pour into the tank) 2% of the total liquid is oil. It is a statement about the final mix, not about the petrol you start with. And this is where people slip up: if you pour 200 ml of oil into your 10 litres of petrol, the can now contains 10,200 ml in total, of which 200 is oil. Work out the percentage: 200 divided by 10,200 = 1.96%. It is not a full 2%.
The simplest picture is a cake with 100 slices: the finished 2% mix is made up of 98 slices of petrol and 2 slices of oil. Your 10 litres from the pump are the 98 slices, not all 100. So to find the 2 slices of oil the right question is: "if 98 slices are worth 10,000 ml, how much are 2 slices worth?", i.e. 10,000 × 2 ÷ 98 = 204.1 ml. Cross-check: 204.1 out of a total of 10,204.1 = exactly 2.00%. That is precisely the calculation made by the Mix Wizard in the carburation app for the Rotax MAX EVO: 204.1 ml per 10 litres.
In practice the difference is 4 ml in 10 litres (half a spoonful), and it is on the protective side anyway: no engine gets damaged by this. But now you know what "2%" really means, why the app gives you a different number from the table, and which of the two is the mathematically exact 2%. Those who want absolute precision use the app figure; the 1:50 table remains an excellent paddock approximation.
The petrol: which one to use
Unleaded petrol from the pump, minimum 95 octane: on track the most common choice is 98, for quality and consistency. In Rotax MAX Challenge races unleaded petrol from 95 to 98 octane is allowed. The requirement almost everyone underestimates is freshness: petrol ages and loses its properties, and the can you prepared a month ago and forgot in the garage is no longer what it was when you made it. Fresh mix, ideally made on the day. One last thing: octane also matters, because engine and carburation are affected by fuel quality (carburation apps also take RON into account). Choose your petrol and stick with it: consistency is worth as much as quality.
The oil: your engine's insurance
You need a fully synthetic racing two-stroke oil, designed for the revs and temperatures of a kart. We use and sell XPS, developed with Rotax: it lubricates where needed and burns clean, keeping the spark plug and exhaust valve in good order. Two golden rules: never mix different brands or types of oil in the same can, and do not be tempted by generic oils: saving on oil is the most expensive saving there is.
How to prepare a good mix
A clean can and a graduated measuring cup. Pour in the oil and shake well: that way the oil spreads straight away. Then pour some petrol into the measuring cup to dilute any oil left in it and pour it into the can. Label the can with the ratio (2% or 3%) and the date: it seems fussy, until the day it saves you. In winter, when the oil is thicker, shake harder and for longer.
Mistakes that cost you an engine
Measuring doses by eye; using mix that is weeks old; lowering the ratio because 'it works the same': it does not work the same. A two-stroke is lubricated ONLY by the oil in the mix, and a lean mix is the fast track to a seizure. And also: dirty cans, water condensation, petrol of doubtful origin. An engine always repays care with reliability.
Frequently asked questions
What oil ratio does the Rotax MAX need?
2% (1:50) for normal use; during running in 3% for the first 10 litres of petrol (0.3 litres of oil per 10 litres). Recommended oil: XPS fully synthetic, developed with Rotax; in Rotax MAX Challenge 2026 races XPS Castor Racing Oil 2T at 2% is mandatory. Remember the explanation above for calculating the percentage correctly.
How much oil in 5 litres of petrol?
According to the Rotax table 100 ml; with the exact calculation on the total mix (the one used by carburation apps) 102 ml. During running in, at 3%: 150 ml. Always with a graduated measuring cup. Remember the explanation above for calculating the percentage correctly.
Is 95 or 98 octane petrol better?
Unleaded, minimum 95 octane: on track 98 is also commonly used for quality and consistency. In Rotax races 95 to 98 octane is allowed. Always fresh: petrol ages.
Can I use mix left over from my last outing?
If only a few days have passed and the can has stayed sealed and in the shade, yes. After weeks or months better not: properties and lubrication are no longer guaranteed.
What happens if I put in too little oil?
The engine works under-lubricated: friction, heat and, in the worst cases, a seizure. In a two-stroke the mix IS the lubrication: the ratio is never reduced.
Why does my app say 204 ml per 10 litres instead of 200?
Because the app calculates 2% of the finished mix: 98 parts petrol + 2 parts oil, so oil = 10,000 × 2 ÷ 98 = 204.1 ml. The quick 1:50 table instead calculates 2% of the petrol alone (200 ml), which in the finished can becomes 1.96%. The app figure is the exact 2% and adds a few ml, on the safe side. Remember the explanation above for calculating the percentage correctly.
Conclusion
The right ratio, fresh petrol, serious oil and a clean can: four rules that take five minutes and are worth an engine. XPS oil and measuring cups are in our shop, and if you have doubts about your mixing routine, message us.
Ratios and guidance checked against official Rotax documentation (2024 edition operator's manual and Rotax MAX Challenge 2026 technical regulations) and XPS.
Questions about this topic?
Message us on WhatsApp: we answer personally, with the experience of people who live at the track. And if you want to drive a real racing kart, with Arrive & Drive you get into one of ours, ready on track. The right spare part? You will find it in the shop.
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Read also: The Rotax engine radiator: the right temperature and how to manage it → · The Rotax engine battery: ignition, starting and care → · Running in a Rotax engine: the right procedure step by step →
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Author: Sergio, TKS RaceLab | Published: 6 July 2026 | Updated: 4 October 2026
TKS RaceLab is the Italian online store dedicated to karting: spare parts, accessories and everything you need to get on track. With Arrive & Drive you arrive at South Garda Karting (Lonato), Franciacorta, Cremona or Ala and find your kart ready to go. No hassle, just driving.
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