Mixing 2 stroke fuel ratios for dirt bikes (premix) can be a royal pain in the jaxi, and more annoying than having to listen to Britney Spears on the office radio. However, it’s essential for two bangers and it’s something you need to do correctly or you’ll damage or even destroy the engine.
A lot of people seem confused about what ratios to mix the fuel and oil at. The safest, easiest and best answer is mix it at the ratio recommended by the manufacturer of your dirt bike. They are the ones who know the engine better than anyone else including your local mechanic.
Keep in mind the ratios the manufacturers recommend are for a high performance dirt bike that is designed to race at its full capacity. If you have skills like Ryan Dungey and you ride your bike at full noise most of the time you need the recommended petrol to oil mix to keep the piston and rings properly lubricated. On the other hand, if you are just pottering around and spending most of your bikes time in the low to mid revs range, that extra oil is probably an overkill and not entirely needed.
The problem with veering away from the recommended fuel/oil ratio is the carburetor is set up for the right amount of petrol/oil/air mixture, so if you significantly alter this ratio you will need to change the jets and carby settings to suit.
My YZ 250 runs at 32:1 which is what’s written in the owners manual. If you don’t have an owners manual, consult your local (Suzuki, Yamaha, KTM etc) dealership and ask them.
A lot of riders run their bikes at 40:1. If you aren’t pinning it everywhere you will get away with this. Just keep this in mind: You will not damage your engine by mixing too much oil with your gas. The worst it might do is foul plugs, although a gunked up carburetor or incorrect carby settings are a far more likely cause of fowled plugs and a smokey exhaust. However, if you forget to mix oil in at all, or consistently don’t use enough you risk wearing out the engine prematurely or seizing it.
Examples of Oil-to-Gas Ratios for Various Bikes
- KTM 50 SX (and Mini) – 60:1
- YZ 250 – 32:1
How To Mix Two Stroke Fuel For A Dirt Bike – Tips And Pointers
- Figure out the correct fuel oil/mix first using the chart below.
- Have a designated oil measuring cup/pouring container like this one on Amazon and keep it clean and free of dirt, water and any other foreign materials.
- Measure the oil accurately into the measuring cup on a flat, even surface. Pour it into the fuel container then tip some of the petrol back into the empty oil measuring cup. Swirl it around to clear away any residual oil. Pour it back into the fuel container.
- Shake the fuel container to ensure the oil is thoroughly blended then pour into your dirt bike fuel tank.
- Don’t use old premix. Manufacturers tell you to mix and use on the day, then throw the rest away. I don’t think you have to be that serious, but throw it away after a couple of weeks, or better yet, pour it into the petrol tank of your car – small amounts won’t hurt it.
- Use only high quality or premium two stroke oil. Castrol, Bel Ray and Yamalube are top brands that produce synthetic 2 stroke oils for high performance motorcycles. You will pay more for a quality 2T oil but the benefits are great. Reduced visible smoke, reduced carbon and varnish deposit build-up, better performance, greater engine protection and longevity. Also, it’s not recommended that you mix two different brands/types of oil together as clotting can result. If you’re going to change oils use up the old stuff first.
- Use only premium high octane petrol/gas (not unleaded).
Two Stroke Fuel Ratio Chart
How to read ratio charts: Ex. 25:1 (pronounced 25 to 1) means for every 25 parts/units of petrol you must add 1 part of oil.
An easy way to work out the right amount is to take the volume of gas in mls and divide it by the ratio you want. E.g You want to mix your fuel at 40:1 and you have 8 liters of gas. How much oil should you use? 8 liters of petrol = 8000 mls / 40 = 200 mls.