Jonte – Page 2 – Small Engine Help

Knowing how the fuel flows The fuel delivery system on small engines is one of the easiest systems to diagnose if you understand the fundamentals. For this discussion I’m going to define the fuel delivery system as “gas tank to carburetor” or “gas tank to EFI - electronic fuel injection”. This section will not discuss carburetors or EFI systems as that will be left for another post. Today's modern gasoline poses overwhelming disadvantages for small engines. Modern gasoline is formulated for a 30-60 life cycle. Once its life span exceeds that 60 day life cycle its condition and performance diminish considerably and it becomes ill-advised to use in small engines. Most gasoline sold at gas stations across the United States features ethanol which is derived from corn. Ethanol is an alcohol and draws moisture from the atmosphere, thus the vented gas tank of a small engine allows water to collect inside your small engine's gas tank when it's sitting in storage and not being used. Scientifically, gasoline and water don’t mix and lead to many problems with small engines not running properly. The ethanol used in gasoline also degrades, breaks down the gasoline lines, and carburetors internal parts. The float bowl of non-working small engines is often the tell-tale sign of why a small engine does not run or operate properly. Oftentimes you get white powder like corrosion sediment or a yellowish gel like matter from the ethanol evaporating from the gasoline sitting in the float bowl of the carburetor. I will share examples of this in another post. You may choose to view this phenomena negatively in that it leads to the demise of many small engines. I choose to see this positively; in that it generates most of the work small engine repair shops receive. As you delve into diagnosing the fuel delivery system of a non-running small engine, remember the phrase “when in doubt, throw it out.” The gasoline left in the gas tank of a small engine has usually gone stale, gone past the 30-60 day life cycle window of use and/or the ethanol separated itself from the petroleum part of its composition and thus wont allow the engine to run using this fuel and this could be your problem to begin with. The first fundamental I’d like to introduce is; a small engine gas tank is a liquid container that has to store, contain and safely transport gasoline in many different kinds of conditions and environments. As the liquid (gasoline) leaves the container (gas tank) it has to have a gas tank vent that lets air into the container as the gas tank is emptying itself of gasoline as the engine is operating and using gasoline from the gas tank. This gas tank vent may come in the form of an air vent directly on the gas tank filler cap or a separate gas tank vent built into the gas tank. If there is no functioning air vent letting air into the gas tank, then the fuel delivery system will vapor lock, its sides will typically cave in as it draws itself into a vapor locked state and gasoline flowing from the gas tank will slow to a dribble then completely stop flowing resulting in the small engine not getting any gasoline for operating and the engine will die or stop running. This first fundamental is extremely important in understanding and never overlooking in becoming proficient in understanding how to diagnose a non-working small engine. Whenever a small engine wont start, one of the first things to check is if there is gasoline in the gas tank. Then “is gasoline flowing from the gas tank through the various elements that make up the fuel delivery system. The small engine fuel delivery system consists of a combination of the following elements. It may or may not contain all of these parts depending on the application and type of equipment it's powering. a gas tank, gas tank filler cap, gas tank vent, gasoline line, gasoline filter, gasoline shut off valve, gasoline pump, The second fundamental in small engine fuel delivery systems is that gasoline does not flow uphill. Hence, most small engines have the gas tank mounted higher than the carburetor or EFI (electronic fuel injection). Most bigger small engines feature a fuel pump to aid with getting the gasoline from the gas tank to the carburetor or EFI system. Small engine gasoline pumps have mostly taken the form of a diaphragm powered gasoline pump that operates off of crankcase vacuum. There are also 12v DC powered low pressure gasoline pumps used in certain conditions. Caution: it's easy to overpower a carburetor's float needle and flood the engine crankcase with gasoline when using an electric fuel pump. It is usually unnecessary and ill advised to go to such a powered pump because of the dangers of overpowering the float needle and flooding the engine crankcase. The most common diaphragm gasoline pumps found on small engines is typically adequate for all situations you will find a small engine used in. In the instances I’ve seen someone modify the original system and go to a powered gasoline pump, it was because they did not understand small engine fuel delivery systems and were not able to properly diagnose it and solve its original problem. By changing the fuel delivery system to a powered gasoline pump, they have now introduced an entirely new problem on top of the original fuel delivery condition. My favorite fuel delivery system diagnostic tip for a non running small engine that is not running due to fuel delivery: if you're doing this kind of repair work frequently, get yourself a small portable gas tank off a small suitcase generator or a string trimmer. Affix a 3ft piece of gasoline line to the gas tank outlet on the bottom of this small portable tank. Temporarily mount with a zip tie or bungee cord this small gas tank higher than the carburetor or EFI system on your non-working small engine. Next we will install the gas line coming from the temporarily mounted gas tank directly to the carburetor or EFI system on the engine we are diagnosing. Pour gasoline in this small temporary fuel tank and see if the engine starts and runs off of gasoline from this temporary gas tank. This easy to do temporary gas tank trick quickly and efficiently determines whether the fuel delivery system of your small engine is the reason for this engine not running or whether it's related to the carburetor or EFI system. Once you’ve derived which it is, pinpointing the problem becomes considerably easier.