See full version: TWO-STROKE TUESDAY: THE ART; SCIENCE OF PRE-MIX RATIOS
What is the best ratio for motocross? If you stick to high-quality lubricants, MXA recommends anywhere between 24:1 and 32:1 ratios for 125 and under bikes. You can run 32:1 to 50:1 ratios in your 250 and Open engines. here
Three things that dictate oil usage: (1) oil quality; (2) engine size and; (3) engine usage. For example, if you are running a model airplane engine, you have a small displacement engine that runs at high rpm. Oil migrates through this engine at a high rate of speed (referred to as the engine’s airspeed). The tiny piston is running at 30,000 rpm, so you need a ratio as high as 10 to 12 ounces of oil per gallon to reach proper lubrication.
What about oils that claim a 100:1 ratio? That ratio is not based on reality. Once you understand oil migration, it is clear that a blanket statement like that doesn’t make sense. here
Now, look at a large engine, like you’d find in personal watercraft (1200cc). It runs in the 7500 rpm range, so the oil stays in the engine 10 to 12 times longer. The oil has a longer migration time. In this case, you could probably get away mixing as little as 2 ounces per gallon. Engine usage has to be taken into consideration, too. The same size engine that is used for motocross can run less oil than if it is used for the high revving sport like or karting. more
The prerequisite for racing a two-stroke is that you have to mix oil in your gas. It is possible to purchase pre-mixed two-stroke fuel from VP Fuels, but most racers mix their own. Companies like Blendzall, Reverend Motors and Maxima all offer various oils and blends depending on your needs and desires. As a general rule, you are trying to find a ratio of oil to gas that works best for your engine and its state of tune. In the 1970s riders preferred to run 20:1 ratios (20 parts gas to one part oil). Over the years this morphed into 40:1 thanks to modern cylinder liners, piston metallurgy and carburetion.
This is due to the piston generating too much heat when moving up and down inside the barrel. more
The improvement in mixing agents and additives to reduce oxidation, corrosion, separation of fuel / oil and cavitation by oil pumping makes these excellent lubricants for Endure, performance scooters and other 2-stroke motorcycles that tend to travel further between engine rebuilds [links]
Vegetable oil, or castor oil, are naturally derived vegetable-based oils used forever and a day. When mixed at high oil to fuel ratios e.g. 20:1 and even higher in petrol, these oils have good lubrication potential, but their inability to remain mixed is a less than desirable attribute. For fast revving engines such as karts and smaller capacity motorcycle engines, vegetable-based oils often have what is called ‘high cling volume.’ Because of the high volume of oil and its normal viscosity, it appears to bind at intense rpm (15,000 +) to the bearing and piston skirts fending centrifugal force effects and aiding in heat dispersion. here
The semi-synthetic oils are a blend of conventional synthetic developments combined with natural oils of greater consistency. In general, the balance of these oils is a bulk of mineral with a small amount of synthetic additives. The oil blender also comes with a cross section of synthetic additives. Many of these have their own specific identity and purpose enabling a more accurate blend of oil to produce the performance and emission requirements accompanied by affordability for the modern 2-stroke high-performance engine. [links]
Engine Protection
Outboard Synthetic 2-Stroke Oil provides premium protection and performance at 100:1 mix ratios. It is formulated for hot-operating two-stroke outboard motors, effectively fighting carbon and deposit formation and preventing ring sticking. [links]
You could try a 75:1 fuel mix more
AMSOIL Synthetic 2-Stroke Oil has been providing improved performance and protection in two-stroke engines since 1973. Trust the extensive experience of AMSOIL, The First in Synthetics®, to do the best job protecting your engine. [links]
Have you tried adjusting the carb low speed mixture .
(Reduce the ide speed to the absolute minimum, lean out the mixture until if falters then enrich it again to just run smoothly. Finally readjust the speed)
If you can find it you could try Amsoil synthetic 2 stroke outboard engine oil at 100:1 ( I'd either fog it or run a tank ful of 50:1 before laying up whatever oil I used at 100:1)
Specifically designed for outboard motors, Outboard 100:1 Pre-Mix Synthetic 2-Stroke Oil contains a heavy dose of low-temperature dispersant additives that excel at reducing varnish, carbon and deposit formation in water-cooled motors. Its low-smoke, low-odor, low-toxicity properties produce fewer emissions at 100:1 mix ratios than oils mixed at 50:1, benefitting operators and the environment. Outboard Synthetic 2-Stroke Oil is formulated to prevent "oil loading" and plug fouling for rapid throttle response, making it ideal for trolling motors. [links]
Smokeless Operation
Outboard Synthetic 2-Stroke oil's synthetic formulation burns cleanly. When mixed at 100:1, smoke is virtually undetectable. Boaters subjected to smoke and fumes benefit from these low-emission properties.
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. here
Dirt bikes make spending time in the great outdoors worthwhile. Feeling the wind whistle through your helmet and hearing the sound of the engine makes everyone feel more alive. That feeling can't.
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.
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. more
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. here