Troubleshoot power equipment
If your power equipment starts hard, runs rough, lacks power or does not run at all, you must troubleshoot the problem-that is, you have to analyze what the problem is. Analysis consists of performing tests and taking specific steps to define the problem. Sometimes the cause of an engine problem is easy to find. Other times, checking out probable causes requires deductive reasoning and using the process of elimination.
Obviously, you should test the simplest and the most probable causes first. If the component or assembly passes the test, continue to test the next-most-probable cause, until you find the defect.
Step 1: Review the service information Before starting to work on any engine, review the manual or troubleshooting chart. Manuals show exploded views of assemblies and systems. These detailed drawings help you disassemble and reassemble parts in the proper order. They also list any special tools necessary to do a job.
Most guides include a troubleshooting chart listing the most common and chronic troubles, along with possible causes and suggested remedies. If you want your crews to use these manuals, however, it's important that you leave them where they are easily accessible.
Step 2: Perform preventive maintenance Storage problems are a primary cause of small-engine failures. But lack of maintenance runs a close second. Here are some procedures to keep your power equipment running.
* Adjust tolerances and clearances properly. Your manual lists engine tolerances and clearances. When checking and adjusting a spark plug, for example, this chart provides the correct dimensions and specifications. Where tolerance specifications show two values, the actual dimension must be within that range. * Monitor the fuel system. With the advent of electronics in today's small engines, many problems are fuel-related. If symptoms point to the fuel system, you'll have to check thoroughly for the source because it could be located in any of several parts. It could involve the fuel pump, the carburetor, the reed valves (in 2-cycle engines), fuel lines, the gas tank or filters. Troubleshooting will involve checking or testing one part after another until you locate the trouble and correct it.
* The fuel pump. If the engine isn't delivering any fuel to the carburetor, and the fuel is gravity fed, check the following: * Is there fuel in the gas tank? * Is fuel flow blocked by a clogged filter? * Do you find much sediment in the gas tank? * Can you see or smell gasoline in the carburetor?
If the engine is equipped with a fuel pump, and fuel is not reaching the carburetor, check the following: * Is there fuel in the gas tank? * Are the fittings tight that connect the fuel line to the tank and pump, preventing the pump from drawing air? * Is the fuel filter clean? Many filters have clear sediment bowls, which allow you to easily see if water or other contaminants have collected at the bottom of the tank. * Is the pump actually working? Disconnect the fuel line between the pump and the carburetor. Turn the engine over a few times. You should see a well-defined spurt of fuel at every stroke of the pump. Caution: Make sure no ignition source is present when you work with gasoline.
Where you suspect fuel-pump problems, make sure the fuel flow from the supply tank is not interrupted before it gets to the fuel pump. A kinked or bent line can allow enough fuel for the engine to idle, but it can cause the engine to stall when you open the throttle.
* The carburetor. If you correct fuel-pump problems but the engine still surges or lacks power, the cause may be poor carburetor adjustment or carburetor defects. Most carburetors have two needle-valve adjustments. A third adjustment is the idle-speed stop screw. Keep in mind that you don't always find needle valves in the same location on the carburetor body. * Adjust the high speed properly. Each engine manufacturer will give a "rough" setting for the high-speed and idle screws. This setting permits the engine to start. You then should run the engine long enough to warm it up before making further adjustments. For the first adjustment: * Open the throttle wide * Slowly turn the high-speed adjusting needle forward then backward slowly * After reaching maximum speed, turn the needle counterclockwise slightly * Leave the engine running a little rich (fast).
* Adjust the idle properly. After the engine is running fast: * Move the throttle to the slow-running position * Turn the idle-adjusting screw slowly, first in one direction and then in the other.
After the idle is smooth: * Adjust the idle-speed stop screw to the recommended setting.
(Note: Not all carburetors have two needle settings, but they all have an idle-speed adjustment. Many manufacturers now omit these adjustment screws to prevent tampering.)
* Clean or replace the air filter. Clean or replace the carburetor air filter before each season of operation and at regular intervals thereafter. A plugged air filter can cause hard starting, loss of power and spark-plug fouling. A torn air filter can destroy the engine quickly.
Remove old oil from oil-bath air cleaners and wash the filter in solvent. Refill with the recommended oil type to the correct level. Don't use gasoline as a solvent. Doing so is hazardous and also creates a toxic-waste problem.
If your engine uses polyurethane-foam-type air filters, wash and rinse them in an appropriate solvent. Evenly distribute about 2 tablespoons of clean SAE-30 oil in the filter material by compressing it in your hand. Under severe dust conditions, clean air filters frequently. If your engine uses a dry canister, replace it with a new one.
Step 3: Adjust the engine governor properly Small-engine-governor designs are of many types-and so are their methods of adjustment. Even so, small engines use only two types of governors: air vane and centrifugal flyweights. The centrifugal-flyweight governor is the most popular. Often, you can determine the method of adjustment by using good judgment and reasoning. Keep in mind that centrifugal force and spring pressure are opposed to each other and work to open and close the throttle.
Step 4: Test the compression Sometimes it is necessary to check further into the condition of an engine. A cylinder compression test is a logical first step toward this. This test is especially valuable if an engine is losing power, running poorly and shows little or no improvement after fuel and ignition checks.
To do a proper compression check: * Run the engine until it is warm * Disconnect all drives to the engine * Open choke and throttle valves wide * Remove the air cleaner * Remove the spark plug and insert a compression gauge * Ground the spark-plug wire by attaching it to a metal part of the engine * Crank the engine and record the readings. Repeat to assure accuracy.
An engine producing a compression reading less than the minimum suggested by the manufacturer usually has one or more of the following problems: * Leaking cylinder-head gasket * Warped cylinder head * Worn piston rings * Worn cylinder bore * Damaged piston * Burned, warped or broken valve * Improper valve clearance * Broken valve spring.
To determine whether the valves or rings are at fault, squirt a tablespoon of SAE-30 oil into the spark-plug hole. Crank the engine several times to spread the oil, then repeat the compression test. The heavy oil will temporarily seal ring leaks. If the compression does not improve, the rings are satisfactory and leakage is due to the valves, the cylinder head or a damaged piston. If the compression reading rises significantly, the leakage is due to defective piston rings.
(Tip: During your annual spring tune-up, take an extra 2 or 3 minutes and give the engine a compression test. Write down this reading in your maintenance book as a log of your mower's performance.)
Preventive maintenance will always be the first step in keeping your inventory of power equipment in top condition. When problems do occur, you can reduce repair costs and downtime by having staff prepared to identify common problems. Diagnosing the problem is the first step in repairing broken power equipment.
Robert Sokol is associate editor of PRIMEDIA Intertec's ABOS Marine Blue Book in the company's Technical Manuals Division. He also is an Automotive Service Excellence master technician and a mechanical investigator for the Overland Park, Kan., police department.
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