Bad Seals, Solenoid Valves : lawn mower

Bad Seals, Solenoid Valves : lawn mower

Bad Seals

O-rings and gaskets can shrink, crack and lose their elasticity over time. Replace any part that shows signs of ageing.

Solenoid Valves

Larger engines, for example, those mounted on the mowers can incorporate a solenoid valve into the float cup. The solenoid is an electromagnet that opens a valve when voltage is applied to the coil, allowing the fuel to flow. Check with a multimeter that the voltage is being applied to the bobbin. (This also applies to starter solenoids.) In addition, solenoids may become clogged, or the valve may become clogged.

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Float, bowl and jet check : lawn mower

Float, bowl and jet check : lawn mower

•     First of all, if there is a gas faucet installed, turn. Alternatively, hold the fuel line with a vise or something similar (this may not completely cut the flow). You can do without holding the line, but don't panic when the fuel starts to run out, in any case it should be just a trickle. Have a container ready and hold it under to catch any fuel.
•     Loosen and remove the nut from the cup (which looks like a bolt, don't ask me why it's called a nut!) At the bottom of the cup, being careful not to lose any fiber washer.
•     Remove bowl completely.
•     Loosen the vise screws or open the faucet and the fuel must flow freely from the inlet valve. Gently press the float up and be sure to cut the flow. If it does not, debris may be blocking the needle valve, which prevents the needle from settling properly. In addition, the float could be drilled and not be able to float properly. Both conditions will cause the carburetor to flood and possibly the fuel outlet of the carburetor air inlet through the air filter.
•     If no fuel came out of the needle valve when the floating container was removed or the fuel tap was activated, there could be two causes. First of all, the fuel filter may be blocked. This can be a separate component in the fuel line or in the fuel line inlet inside the tank. The second cause is a blocked valve that prevents the fuel from flowing into the container, so it should be cleaned. If the container is slowly filled due to a partially blocked inlet valve, the symptoms are a lawn mower that starts and then dies after a couple of minutes as the fuel is consumed faster than it can flow into the container from the T Anque. Another possibility in larger engines, such as lawn mowers, is a fuel pump that is not working properly.
•     If there seems to be no problem with the flow of fuel in the container, the fault could be a clogged main fuel jet. If you have an air compressor, you can try to blow through the jet with an air pistol. However, it might be gummed up, and in this case you may try using an aerosol carburetor cleaner. Insert the flexible spray straw into the stream and use some puffs to clear any debris. Do not use steel wires, pins or needles to hit the jets, as soft bronze surfaces may be damaged (in theory, the soft copper wire strands of a power cord should be fine because they are softer than brass).
•     Finally, remove any debris from the Filter cup and check if the nut in the brass box is clogged by dirt. In some carburetors, this performs two functions, keeps the container in place and also acts as part of the jet system. Once all this has been done, replace the cup, being careful not to overtighten the Brass cup nut and try to start the engine again.

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Fuel line, Floating Bowl type Carburetor, How Float Bowl Works : lawn mower

Fuel line, Floating Bowl type Carburetor, How Float Bowl Works : lawn mower

A bent or obstructed fuel line between the tank and the Float cup can restrict the flow of fuel to the engine.

Floating Bowl type Carburetor

If the fuel tank is located above the carburetor, it is likely to be float type. (See photo below)

Dirt and gum are the carburetors ' greatest enemies, as they can contain several narrow passageways through which the fuel flows. Over time, rubber deposits can reduce these passageways. In addition, the tiny dust particles contained in the fuel will bypass a fuel filter and be directed to the carburetor. This can also obstruct everything. A patented carburetor cleaner can be used to clean everything.

How Float Bowl Works

The float and bowl function as a toilet cistern, keeping the fuel at a constant level so that it can be sucked into the carburetor. Float buoyancy causes it to rise. When the gas in the container reaches an established level, a needle at the top of the float is forced into a valve seat, closing the fuel inlet to the container. Without this system, the gas would simply feed by gravity to the carburetor, flooding. If the lawnmower does not run for more than a few minutes, the float Cup may not be filling or filling very slowly. If it is slowly filled, the mower is cut, but can often be restarted after it has been left for a while (because the container refills).

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The choke : lawn mower

The choke : lawn mower

The choke is simply a flat disc mounted on a shaft at the carburetor air inlet. When you turn on the choke, the shaft is rotated so that the disc blocks the airflow, and there is greater suction in the inlet. This makes it possible to vacuum more fuel and also makes it easier to start. Chokes are usually automatic but can be manual on some engines. In this case, they must be turned on when starting an engine and then turned off after the engine has been running for several seconds. If an engine is hot, leaving the choke will probably flood the carburetor and cause difficulty starting.

Carburetor air intake showing choke plate (air filter has been removed) on a small 3 1/2 HP Briggs and Stratton engine.

Carburetor Air inlet showing choke plate (air filter removed) on a small 3 1/2 HP Briggs and Stratton engine.

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The air filter or cleaner : lawn mower

The air filter or cleaner : lawn mower

The function of an air filter is to remove dust, sand, grass and other dirt from the air stream before it enters the engine. Without a filter, this material would scrub the piston and cylinder, causing premature motor wear over time. Dirt will also clog small streams that flow from fuel from inside the carburetor.

The air filter must be clean for optimum engine operation. A dirty, clogged air filter will deprive an oxygen engine, causing a reduction in power, excessive fuel consumption or carburetor flooding, and difficulty starting. The foam elements can be washed with hot water and soap to remove oil and dirt. Then squeeze the dry foam into a cloth. Pour a teaspoon of motor oil into the foam and massage evenly through the element (the function of the oil is to catch the dust passing through the foam). It is possible to clean some of the dust from a paper filter blowing from the inside with compressed air. However, this type of filter should ideally be replaced.

• Paper air filter.
• Foam air filter.

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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.