A fairly common oil-related failure happens when a 2-stroke sled is brand-spanking new. Sometimes, even if there is plenty of injection oil in the oil reservoir, there is air in the oil lines and the pump cavitates for a while, purging the air out of the system. Sometimes this condition will pass, sometimes it wonâ€™t, but it can cause a period of time where insufficient oil is reaching the engine internals. With a brand new tight engine, this is not a good thing. This is why youâ€™re (almost) always told to run some oil in the first tank of gas at a ratio of 100:1, so the engine gets lubrication during this time period (and why set-up technicians are supposed to bleed the air out of the lines before delivery). With 128 ounces to a gallon, this means one ounce per gallon and youâ€™re fairly close. We figure 13 ounces per ten gallons of fuel, or 15 ounces per 12 gallon tank.
So when you take delivery of your new 2-stroke sled, you want to know if any oil has been added to the gas, and how much. Some dealers donâ€™t add any; some add a gas and oil mixture that is at the specified 100:1 ratio (but not a full tank) and some will add a splash of gas, but a full 10-15 ounces of injection oil so when you fill the tank with gas you will be close to the 100:1 ratio. In this case, if you didnâ€™t know what they have already added and you add yet another 10-15 ounces youâ€™ll have a smoking machine for that first tank! And, quite possibly, a gooey set of spark plugs.
Bottom line, you do want this oil in the first tank of fuel to help smooth the internal engine surfaces during engine break-in, as the moving parts get used to each other and take off the high spots of the surfaces. Typically, using synthetic oils during this period tend to lengthen the amount of time it takes an engine to â€œloosen upâ€. Each engine acts different; some donâ€™t change that much, some really are tight to begin with and the difference is quite profound after a few hundred miles. 4-strokes seem to take even longer to break-in that the 2-strokes.