There have been many questions and misconceptions regarding the mixing of 2-Cycle Fuel that is used in most chain saws, trimmers, and other small handheld equipment. I am hoping that I can clarify some of these issues. Two-cycle engines require the mixing of oil with fuel. This oil is needed for internal lubrication of the engine. Unfortunately this oil is not good for the combustion process. This is one of the inherent issues with two-cycle engines is the poor emission quality. The EPA has been strong in its regulation on how much emissions these units can produce. These regulations have been causing manufacturers to create leaner and leaner running engines. Lean engines have less oil in the fuel mixture that what there were in the past. I remember seeing fuel ratios of 16:1 and 24:1 years ago. A 16:1 ratio translates to 8oz of oil to every gallon of fuel. Now, most manufacturers are running 40:1 or even 50:1. This is 2.6oz of oil to every gallon of fuel.
Where some of the problems are now arising is having to retrain the users of the older equipment. It was no issue to add a little extra oil to the fuel in the older models. This would just help in increased lubrication. The engines at that time had larger orifaces in the carburetors, larger exhaust ports, and the manufacturers tolerances inside the engine were not at tight.
Now, these newer engines are running ALOT leaner, the orifaces in the carburetor are smaller, and exhaust ports are smaller. The addition of extra oil causes many problems. This oil does not burn properly, causing the unit to smoke. Continued use of a rich mixture will cause carbon buildup within the exhaust port. As the piston moves up & down past the port, this buildup can break off & fall back into the combustion chamber. If this carbon gets between the cylinder wall & piston, it will score the cylinder walls & exhaust face of the piston. After continued use, compression is lost and the engine will no longer operate. This damage can occur very quickly if not caught.
Ok, after hearing all this, one might think to use a little less oil. NO NO NO. Now, there is not enough adequate lubrication, the engine heats up more that normal, metal expands more than it should & you begin to cause damage throughout the cylinder.
The best advise I can give is to follow the manufactures recommendations that are listed in the owners manual & mix the proper ratio that your unit requires. There are some companies that have actually gone and done the work for you and you can purchase pre-mixed fuel. This is great, because you will be using the correct ratio fuel, and these fuels are usually ETHANOL-FREE!!! Ethanol is a whole other problem that we will try to address in another post.
