Old gasoline & octane levels, what you need to know?
Old gasoline is the number one cause for small engine repairs.
Most small engine manufactures consider gasoline stored in small quantities in fuel tanks or gas cans to be old after 2 months. Old gasoline can damage fuel system parts, cause engine running problems or completely destroy your engine. Its not recommended to store fuel in your equipment or small gas cans for more than 2 months. Gasoline will lose octane as it ages. Example...91 octane may become 90 octane after 60 days. High octane fuels resist damaging pre ignition & detonation better than low octane fuels. That's why hotter running high performance engines usually require 91 or higher, otherwise they may overheat. Some models of outdoor power equipment require 91 octane fuel, but most only require 89 or 87. During very hot weather engines may need higher octane fuel than normally required. Running old gasoline leaves hard to remove deposits in your engine. In a two cycle engine deposits gum up the piston, rings, cylinder & crankcase. It can cause a loss of compression or lock up your engine. In engines with valves it gums up the intake valve and may cause the valve to stick. A stuck intake valve can destroy an engine. Gasoline becomes less volatile & more acidic as time passes. Acidic gasoline damages fuel systems, mostly the rubber parts inside carburetors plus the fuel hoses & tank grommets. Some two stroke carburetors have small rubber check valves built into them that cannot be replaced, so the entire carburetor will have to be replaced if damaged. As gasoline evaporates it can leave behind a varnish residue or small particles that clog fuel filters & carburetors. Every summer when our temperatures in Las Vegas rise over 100 degrees certain equipment types & models come in running hot, lean or dying & making a strange noise. The strange noise is engine knocking caused by pre-ignition, that's when a red hot piston dome or very high temperatures in the combustion chamber ignite the fuel mixture before the spark plug fires. Pre-ignition & detonation can destroy your engine. The very popular Echo PB770 backpack blower is one example. They can run extremely hot, lose power, die, detonate or seize while using anything less than 91 octane during hot summer months. But during the rest of the year they may run fine. Sometimes a lean condition can be caused by a clogged fuel filter, clogged or worn carburetor, leaking gaskets or seals. But don't overlook old fuel, poor quality fuel or low octane levels. Expensive pre-canned ethanol free fuels that come with 93 octane and a 5 year unopened shelf life are a better choice for multiple reasons. But beware sometimes they don't hold up as advertised. We have seen brand new cans of fuel that would not ignite or burn in a new engine. We have also seen some cans turn bad just a few weeks after opening. Sometimes poor quality fuel can run ok in one type of equipment but perform very poor or not at all in another. If your small engine starts running hot, lean, stalling, dying or is making an unusual noise especially during hot weather we suggest trying a fresh tank of 91 octane or higher gasoline or fuel mix depending on the equipment. Do not use fuel that contains more than 10% ethanol, it can damage your engine. Inspect the spark plug first, the tip of the electrode where the spark occurs normally burns between clean, tan or black, a white burning electrode tip or tiny balls of ignition fouling deposits on the electrode tip are a good indication it's running extremely hot. One last note if you're filling a small gas can at the pump. Please be aware, the last person at your pump may have purchased 87 octane. You may be getting some 87 octane in your gas can, maybe as much as a half gallon before the 91 your paying for comes in. To avoid this you can pump some into your vehicle before filling your gas can.
Tec tips from Rec World Inc. are not necessarily the exact advice of any single one of our manufactures.