Water in the tank : lawn mower

Water in the tank : lawn mower

•     Water in the fuel tank can cause the motor to agitate and lock. Maybe you left your lawn mower exposed all winter, causing the water to seep through the vent on the tank lid, or you could have gotten bad fuel from your gas station. Leaving gas in the tank during the winter may cause moisture to accumulate, especially if you use fuel with an ethanol content. Ethanol attracts some moisture that normally exists as a suspension in the gas (such as cream in the milk). If you leave a lawnmower sitting for months, it may eventually settle down to the bottom of the tank, and only a couple of teaspoons may be sufficient to cause difficulties at the start.
•     The water is denser than the gas and will sink to the bottom of the tank. If you light a flashlight inside, you can see water globules at the bottom (a maglite is useful for this kind of thing because the beam can be focused to light the bottom of the tank).
•     If you drain the gas tank, you may use a cloth or sponge pushed to the end of a long screwdriver to absorb any remaining water at the bottom of the tank. If a lot of water has accumulated at the bottom, it may also have passed through the fuel line in the carburetor. In this case, you must remove the floating container as described below, and drain the contents of the container plus whatever is left in the fuel tank.

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The carburetor : lawnmower

The carburetor : lawnmower

If the ignition system is OK, you must check the fuel system below.

Books and troubleshooting guides often advise you to check if the fuel is actually coming to the engine by removing and examining the spark plug after several pulls of the starter cord. It must be moist, but a damp plug indicates flooding. However, at the time the plug is removed and if the weather is warm, any moisture can evaporate, so this is not a totally reliable method to identify a problem with the carburetor.

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The fuel flows from the tank to the carburetor. The function of this device is to create an explosive fuel mist mixed with air, which is aspired to the engine to burn it and provide energy. An air filter cleans the incoming air to prevent malfunction and damage to the engine. Several problems in this section of the engine can cause starting difficulties or loss of power.

These include:

•     Dirty air or fuel filters
•     Clogged jets
•     Parts that are badly sealed
•     Punctured or worn components
•     Moving Parts sticking
•     Water in the tank

Diagram of a carburetor
A carburetor filters air and mixes it with fuel, forming a fine mist which gets sucked into the engine.
A carburetor filters the air and mixes it with fuel, forming a fine mist that is absorbed into the engine.

Carburetor seal or O-ring

The carburetor must be properly sealed with the motor screws or tightened, and the O-rings must not wear out or be damaged.

Test the correct functioning of the points and establish the gap : lawnmower

Test the correct functioning of the points and establish the gap : lawnmower

•     Connect a probe or alligator clip to the condenser.
•     Connect the other probe to the rocker.
•     Set your multimeter to the lowest resistance range.
•     With the controls on the mower in the "on" position, and with the open points, the resistance must be less than one ohm and is effectively the resistance of the Magneto's primary coil and the cables of its serial meter.
•     Now turn the crankshaft until the points are closed. The resistance should now fall to a lower value and is only the resistance of the wires. The point gap is set by releasing a screw and moving the capacitor, or by turning a screw. The gap should typically be 0.02 inches, but check the specifications for your engine to get a specific value.
•     If you get a weak, thin, and not very blue spark, the capacitor (capacitor) may be defective. It is not possible to test this component without a special equipment, however, if you test it with a multimeter set to a low ohm range, a short capacitor will have a definite resistance. A good capacitor should give an open-circuit reading, i.e., usually an overload reading that is displayed as "1" on the display.

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Steering wheel Removal of lawnmower

Steering wheel Removal of lawnmower

•     First, remove the balls from the ratchet mechanism piece. Check that they are not rusted and locked in the mechanism, and then add some light oil to the balls when replacing them.
•     Then use a socket wrench (Stillsons) to remove this piece that is held in the flywheel. Loosen it counter-clockwise.
•     Do not press the terminals if they break. I used a flat steel bar under the flywheel wedged against the engine body to immobilize it. (Actually, there is a special tool to hold the steering wheel.) Do not insert anything into the flywheel flaps, which may end Arrancándolos if excessive torque is required to loosen the accessory.
•     The flywheel is fitted on a conical shaft and there is a special extractor available to remove it. You're not supposed to do this, but if you keep touching the bottom of the steering wheel with a light hammer, it should be easy to release. (Gently touch the thickest part with the magnet, but do not hit hard!)

1. Use a pipe wrench (Stillson) to remove this piece. Keep the jaws away from the screw lugs to avoid damaging them.
2. Use a pipe wrench (Stillson) to remove this piece. Keep jaws away from screws to avoid damaging them.
3. Lightly tap the flywheel all round the perimeter to release it. First tap the heavy part with the magnet inserts as shown, and the similar piece on the other side. Don't lose the iron key in the flywheel shaft.
4. Tap the steering wheel around the perimeter to release it. First touch the heavy part with the magnetic inserts as shown, and the similar piece on the other side. Do not lose the iron key on the steering wheel shaft.
5. Ideally, remove a flywheel with pullers.
6. Ideally, remove a flywheel with extractors.
7. The points are inside this compartment.
8. The dots are inside this compartment.
9. Points and capacitor (originally called a condenser): If the rubber seal on the crankshaft is faulty, oil can accumulate in this compartment and splash onto the points, causing misfiring.
10. Clean any tarnish and pitting from the points with a file or fine sandpaper. Take care, as the points are coated with special material to withstand arcing. If you overdo it with the file, you'll end up removing the coating.
11. Finally, remove any residue or oil with a piece of cloth.

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The points gap is set on this Briggs and Stratton engine by loosening the bolt and moving the capacitor. It should be about 0.02 inch (check it with a feeler gauge).

What happens if my lawnmower still doesn't turn on?

What happens if my lawnmower still doesn't turn on?

Read on to get more troubleshooting, but try all the earlier simple things before moving on.

Cleaning points on an old engine

Most modern engines have an electronic ignition system. According to Briggs and Stratton, this usually applies to engines manufactured after 1983. The engine below is probably about 40 years old and the points need to be cleaned.

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• Dirty contact points can prevent a spark from occurring in the plug. The points on a motor are basically a switch that opens when the current through the coil of the spark generator device (ignition coil or magneto) is at its maximum point. This creates a voltage spike in the spark plug. These points can be stained or corroded and bored over time and should be cleaned. A rubber oil seal is installed at the crankshaft exit point from the sump and top of the engine block. If the engine tends to fail (no sparks occur in a cycle), it may be due to the oil getting out of this seal and splashing over the dots. A puddle of oil in the point compartment is evidence of this. It's kind of like a test to get to the points that are usually under the steering wheel of the engine.
• This mower has been stored in a leaking shed and rusted up for over 20 years without being started. I'm going to check out the points and carburetor to see if it's ok. This machine has a pump-and-weir type carburetor.
• This mower has been stored in a leaky shed and has rusted for more than 20 years without being torn off. I'm going to check the points and the carburetor to see if they're okay. This machine has a pump-type carburetor and weir.
• First, remove the mesh on the flywheel.
• First, remove the mesh on the steering wheel.
• Prise off the plate covering the ratchet mechanism.
• Award plate covering the ratchet mechanism.
• Remove the steel balls which form part of the ratchet mechanism. If they are rusted, clean them with fine wire wool and add a little light machine oil when replacing.
• Remove the steel balls that are part of the ratchet mechanism. If rusty, clean with fine wire wool and add some light oil to the machine when replacing.

Magneto coil test on Old point engines of lawn mower

Magneto coil test on Old point engines of lawn mower

The resistance of the secondary coil (which is connected to the spark plug) can be measured with a DMM (digital multimeter). If you do not know how to use one, read How to use a digital multimeter (DMM) to measure voltage, current and resistance.

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•     First, you must connect the sensor probes between the two ends of the coil. One end of the primary and secondary coils is grounded, so connect one probe to the motor and the other to the end of the spark wire. This should give a reading between 2.5 and 5 Kiloohmios. However, this does not necessarily mean that the coil is fine, as the high voltage could be being traced to ground through an insulation failure. However, an open-circuit reading indicates a fault.
•     Check the grounding from the end of the coil to the engine block. It is likely to be a ring crimping terminal, so make sure that it is properly connected and that it is not an open circuit at this point. The resistance of the primary coil must be approximately one ohm, decreasing to less than one ohm as the flywheel is turned, causing the points to close.
•     If the resistance does not change when the steering wheel is turned, the points may be missing. Make sure the motor is in the start position (which opens the off switch) during the measurement. Otherwise, the kill switch cortocircuitará the coil, giving a false reading.

Electronic ignition/Capacitor discharge ignition (CDI)

Electronic ignition/Capacitor discharge ignition (CDI)

Today, engines have an electronic ignition system known as capacitor discharge ignition (CDI) and modules may fail, requiring replacement. If the ignition coil does not produce a spark after testing a new Plug and has checked the power switch to make sure it is not short-circuited, there is nothing else you can do but replace the module.

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Wiring and connections lawn mower

Wiring and connections lawn mower

If a spark is not obtained, inspect the motor wiring. As in a car, the ignition system uses the engine block as a ground, so make sure all the ring notches are tight and not loose. Damaged insulation can short-circuit the voltage to the engine block. The swords can be detached, and the screws holding the ring can be loosened due to vibration.
Check for loose or dirty connections.

The Kill Switch

If you still can't produce a spark, there might be a problem on the kill switch. This shuts off the motor by shorting the magneto coil and prevents a spark from being created when the mower is turned off. The switch works when you release the "Dead Handle" on the mower or put the throttle in the stop position. Trace The wire on the magneto coil to find this switch. You will most likely need to remove the hood from the top of the engine and possibly the steering wheel to check this.

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Check the switch using the continuity or lowest ohm range on your meter. The switch must be in the open circuit when the engine is running and there is a shorting when the motor is off. Remove one of the connections to the switch when checking. Otherwise, the resistance of the magneto coil will give a false reading.

The ignition system: the best place to start troubleshooting

The ignition system: the best place to start troubleshooting

The function of the ignition system is to create a spark on the plug and Ignite the fuel/air mixture in the cylinder. A device called Magneto generates high voltage, and any of the mechanically operated points or an electronic switch will trigger the spark at the appropriate time in the four-stroke cycle.

More than 90% of the time, problems with gas engines are due to a carburetor problem. However, the spark plug is easy to check first.

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See the ignition system diagram below.
The Magneto

On a push mower and other battery-free motors (such as chainsaws, trimmers, and motorcycles without batteries), a device called Magneto is used to generate the high-voltage spark. Magnets are even used on aircraft with a piston motor for safety reasons, so the failure of the battery or alternator does not cause the engine to cut. A magneto is a sort of crossover between a generator and a transformer and has a primary and secondary coil.

The magnet is mounted by the steering wheel (the thing with fins on top of the mower, which rotates). A magnet embedded in the edge of the flywheel induces a current pulse on the primary coil as it moves rapidly beyond the magneto poles. When the current reaches a peak, a set of switch contacts called points is opened, interrupting the current. This causes the magnetic field in the primary coil to collapse rapidly, causing a voltage spike in the secondary coil. This coil, which has many cable turns, increases the voltage to approximately 10,000 volts (or more). A capacitor, also known as condenser, absorbs the current produced by the primary coil allowing the magnetic field to collapse rapidly. The modern engines have electronic ignition and the points are replaced by an electronic switch called thyristor or SCR (silicon-controlled rectifier).

1. Some engines (such as those used in the ride mowers) do not have magnets, and instead will use an on-board battery and a ignition coil to produce a spark, similar to a car's system.
2. Schematic of lawnmower ignition circuit with mechanical points. The points are connected to the primary of the magneto, the spark plug to the secondary.
3. Diagram of the lawnmower's ignition circuit with mechanical points. The dots are connected to the magnet's primary, the spark plug to the secondary.
4. Modern engines have electronic ignition and there are no points to clean. If the ignition module fails, the complete unit needs to be replaced.
5. Modern engines have electronic ignition and there are no points to clean. If the ignition module fails, the entire unit must be replaced.
6. Engine flywheel, visible when the cowling or cover over the mower is removed.
7. Motor flywheel, visible when the fairing or cover is removed on the mower.
8. Flywheel, magneto, and governor vane.
9. Steering wheel, Magneto and governor's paddle.
10. Spark Test on Plug

•     First, verify that the wire that feeds high voltage to the spark plug should not be loose and must be snug. Sometimes the cable may come out of the rubber sheath and the terminal that pushes toward the spark plug. Then, using a spark plug wrench, remove the plug, replace the plug cable into the plug, and place the threaded part of the plug in contact with the motor block to ground it.
•     Now pull the starter cable and look for a spark. You must keep the plug tight against the motor in some way, as it may bounce when you pull the starter cord. This is where an assistant can be useful as it can be difficult for you to see the plug from where you are pulling the starter cable. Try pressing the plug against the lawn mower with a plastic piece or similar, such as a plastic garment peg. The cable could hold the plug, but if it is wet or if the insulation is bad, you may end up getting shocked!
•     If you do not see a spark at this point, there may be a crack in the stopper insulation or it may be dirty and should be cleaned with an old toothbrush and a little gasoline. A wire brush the size of a toothbrush is even better. Let it dry and try to light a spark again. If you are not successful, try another plug and check again. It does not hurt to have a replacement plug for this purpose or to use a car plug, but do not use this plug on the motor unless it is the correct type, as it could hit the piston and cause damage if it is too long.
•     The external electrode of the plug must be filled with a small file if it has been rounded. The spark plug space should usually be adjusted to 0.030 "(30 thousandths of an inch)/0.75 mm, but check your engine manufacturer's recommendations. The separation is measured by a thickness gauge (see photo below). These are generally in the form of a set of steel strips of varying thickness of approximately 0, 002 inches to 0, 030 inches.

    Caution: The threads on a plug are steel, but the engine block and cylinder head are usually aluminum alloys, which is smoother than steel. So that the threads can be damaged if you are not careful. Check for dust or other particles on the plug or motor threads before screwing. Make sure the plug does not kink and do not overtighten. Ideally, you must use a torque wrench to tighten the cap or when you replace the blade on a lawnmower.

If you damage the threads and the plug does not tighten, you can obtain a Helicoil installed in a repair shop. This involves hitting the stock and screwing an insert into place that has internal threads to fit the plug.

If the starter cable is difficult to pull, slip or roll

If the starter cable is difficult to pull, slip or roll

If you find it difficult to remove the starter cord, there are three possible causes:

•     First, groups of wet grass or moss can clog the bottom of the platform and prevent the blade from spinning. Before removing clippings and attempting to rotate the blade to clear the platform, disconnect the spark plug wire.
•     The flywheel brake may prevent the motor from turning. When you release the "Dead Man's Handle" on the mower handle, a switch shuts off and shuts off the engine. A brake is also triggered in place and reduces engine speed. If this brake has been seized in place or the cable that operates it has been broken, this will prevent the motor from turning. You will need to remove the fairing at the top of the motor to get this brake.
•     Recoil starters on some engines have approximately half a dozen steel balls that act as part of the ratchet mechanism. These can rust and cause the starter motor to slide and do not start the engine or prevent it from rolling properly. You can clean the balls with fine-wire wool: Add a light jet of oil to the machine in the compartment housing the balls when replacing them. (Scroll down for instructions.)

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Lawn mower adjustment and Troubleshooting: Basic Hand Tools required

Lawn mower adjustment and Troubleshooting: Basic Hand Tools required

•     Set of tube keys. Inch sizes for American and metric engines for European or Japanese engines. You don't need to spend a fortune on a game because you're not going to use it every day. However, do not buy waste because you can use them to work on other equipment. A 3/8 inch ratchet is fine, or a smaller size of 1/4 inch for use in confined spaces.
•     The combined Keys, open at one end and the ring at the other end, are also useful. These can be used for situations in which a nut needs to be undone, but the threaded section of the screw extends too far beyond the nut to fit into a socket. The keys are also known as spanners in the UK. It is not necessary that the sockets or keys are greater than 3/4 of inch AF (in the planes) or 19 mm of size.
•     Plug wrench to remove spark plugs.
•     Screwdrivers. Flat head and Philips, both large and small.
•     Magnetic Tray This is useful to prevent all those small parts from coming out without authorization!
•     Torque Wrench to tighten the bolt that holds the blade and spark plug.
•     Thickness gauge to check the distance between the spark plugs or the dots.

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Note: Tuning an engine refers to the engine adjustment process for optimum performance. This includes adjusting the spark plug and point gap and adjusting the fuel/air mixture and idling speed.

• Combination wrenches (spanners) - Open at one end and ring at the other
• Combined keys (spanners): Open at one end and ring on the other
• Long nose pliers, flat blade screwdriver, Philips screwdriver, and socket wrench.
• Long-nosed pliers, flat-tip screwdriver, Philips screwdriver and socket wrench.
• Two styles of plug wrench: Socket wrench and box wrench/spanner.
• Two styles of pin wrench: socket wrench and box spanner/spanner.

Before dismantling

Before you begin to dismantle everything, take some high resolution photos with a digital camera if there is any chance that you forget to forget how to reassemble the pieces.

In addition, if you need to remove many washers, bushings, springs and nuts on an axle or bolt, you can thread them into a piece of cable to track the reassembly sequence.