Old gasoline & octane levels, what you should know?
Old gasoline is the leading cause of small engine failures. Many small engine manufactures consider gasoline stored in small quantities inside fuel tanks or fuel cans to be old after two months. Old gasoline can clog or damage fuel system parts, cause engine running problems or completely destroy your engine. Gasoline evaporates, it can leave behind a gummy varnish residue and/or small sand like particles. Either one can clog fuel filters, fuel pumps, injectors & carbs. Fresh new gas will not dissolve varnish or particles, a carburetor cleaning chemical is required. On the popular Honda EU2000 generator a clogged carburetor jet will usually cause the engine rpm's to fluctuate while running, plus the engine may die when a load is applied to the generator. Most of the time the fuel tank needs to be flushed out & the carburetor needs to be cleaned to remove the varnish. We use a heated sonic tank with cleaning solution for cleaning carburetors and a chemical for dissolving varnish in fuel tanks. Running old gasoline in your engine leaves behind varnish that can destroy it. In two cycle engines varnish gums up the piston, rings & crankcase. It can cause a loss of power, loss of compression or seize your engine. In engines with valves it gums up the intake valve and may cause the valve to stick while running. A stuck intake valve can destroy an engine. Gasoline becomes less volatile & more acidic as time passes. Acidic gasoline damages rubber fuel system parts like primer bulbs, fuel hoses, grommets, fuel pumps & internal carb parts. Some carburetors have small rubber check valves built into them that cannot be replaced, so the carb will have to be replaced if damaged.
Octane, 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 hot weather engines may need higher octane fuel than normally required or they may overheat. Every summer when our temperatures in Las Vegas rise over 100 degrees certain equipment types & models come in for repair because they're running hot, losing power, dying and making a strange noise. The strange knocking noise is caused by pre-ignition, that's when a red hot piston dome or very high temperatures in the combustion chamber ignite the incoming fuel before the spark plug fires. Pre-ignition & detonation can destroy your engine. The very popular Echo PB-770 backpack blower is one example. They can run extremely hot, lose power, die, detonate or seize while using anything less than 91 octane during the summer months. But they may run fine on 87 through Fall, Winter & Spring. Sometimes a hot, lean condition can be caused by leaking gaskets, leaking seals, clogged fuel filters or badly adjusted, clogged or worn carburetor. A hot engine can also be caused by dirty and clogged cooling fins on the block or a damaged fan wheel. Just don't overlook old fuel, poor quality fuel or low octane levels. Expensive pre-canned ethanol free fuels with around 93 octane and 5 year unopened shelf lives are a better choice for multiple reasons. Beware, sometimes canned fuels 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, loses power, is stalling, dying or is making an unusual noise especially during hot weather we suggest trying a fresh tank of 91 octane fuel or higher. Do not use fuel that contains more than 10% ethanol ( or ) E85 gasoline, they will most likely damage your engine.
Diagnose, If you want proof it's overheating remove the spark plug and inspect it. The tip of the electrode where the spark occurs normally burns clean or has tan or black carbon on it. If the electrode tip color is white and/or has tiny round balls of ignition fouling deposits on the electrode it's very good evidence it's running too hot. When your engine is overheating the dark carbon deposits on the plug turn white. Don't confuse burnt white carbon with the white ceramic portion of the plug itself.
One last note, if you're filling a small gas can at the pump and need 91 octane, be aware the last person at your pump may have purchased 87. 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. Technical tip by Mark.