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Small engine repair includes many types of small engines and 2-cycle engines. Among these small engine repairs, include lawnmower engine repair, weed eaters, edgers, blowers, generators, and many small motorbikes.
While most small engines are about the same in general design, there are two main types of small engines. The first type of small engine are those with an oil reservoir, and the other use oil mixed in their fuel to lubricate the system. The second type of small engine is commonly called a 2-cycle engine, and uses 2-cycle oil in the fuel. The fuel burns off and leaves oil behind that coats the moving parts and drains down the piston into the crank case. With these small engines, the oil is constantly changed as it blows out in the exhaust, where other small engines with oil reservoirs require an oil change and may have a safety switch to kill the engine if oil gets too low. This prevents freeze-up of the engine due to damage.
This is a common problem with small engines that don't start or suddenly shut-off, but is easily
corrected or prevented by checking and changing oil regularly, and in some cases, replacing the safety switch or fuse. However, this is a
benefit over 2-cycle engines that rely on
mixed oil and gas to operate.
Running 2-cycle engines with higher ratio of oil in the fuel will keep things better lubricated,
but reduces speed due to less fuel burning and blows more oil out the exhaust. This may cause the small engine to smoke.
The flip side, when the fuel is mixed lean on oil, increases speed and strength up to a point. The problem is not enough oil
to lubricate the small engine. This will score the piston and head, lose compression, and lock-up or increase drag due to friction
in the engine. This damage requires replacing the head and piston or more often the whole engine. So if using 2-cycle fuel mixtures,
be sure to use the correct mixture for the engine, and remember to shake the fuel to mix before re-fueling. This will prevent most
major damage to your small engine.
The other major differences between small engines and large engines are the starting mechanism and how they are
cooled. Most larger engine are electric start and liquid cooled, but small engines are generally air cooled and may have a manual
starting mechanism such as a pull-start or kick-start.
With water cooled engines, they can overheat due to low coolant, reduced or no movement from the pump, or by limited air-flow, but
in small engines with air cooling, there is less chance for overheating. The oil reduces friction and circulates to assist in
cooling the engine, and the case of the small engine and head are designed with larger surface area and heat-sinks to allow more
air-flow across the surface. As long as there is good lubrication and oil, and the surface and heat-sinks are clean (generally
dirt, oil, and grass build-up), your small engine should not overheat.
Manual starting mechanisms such as kick starter and pull starters are fairly simple devices designed to
engage in one direction
and release. If they break, you may need to remove a few bolts to remove the device, and replace a plastic or metal gear or spring.
In the case of pull starts, you may need to rotate the pulley as though the rope were fully pulled, and replace the rope before
allowing the re-coil of the pulley, and re-install the pull starter.
With all electric starters, they still have the gears to engage the small engine and release, and they may need replaced.
Depending on your unit, the gears may be available or you may need to replace the whole starter. Electric starters require
electricity. This may sound stupid, but often is the problem with getting one to work. If your starter is not working, you need
to confirm the starter is getting power, and enough of it.
You can start by checking your battery is fully charged with a battery charger. If your battery is good, you can check
for power to the starter by trying to start the small engine while using a test light on the positive and ground of the starter.
If this is difficult, you may need to remove the starter (generally 2-3 bolts) and secure it safely where you cannot get in the
gears, and the starter cannot jump when turned. Then you can apply direct power to the starter to confirm it works. If not,
replace the starter, but if it works, your problem is between the battery and starter for your small engine and repair will require
tracking down the damaged circuit. This can be a battery connection, broken or loose wires, loose ground wire, fuse, or the switch
or key switch. In most cases, it is a fuse or ground wire, but can be a safety switch preventing power. These may include oil safety
switch, a clutch or brake sensor, some seats have a switch under them, or on riding mowers there is a safety switch for
engaged
blades. Any one of these switches can prevent the flow of power, but many don't effect the starter, but rather the spark. So if your
starter is working fine but the small engine won't start and needs repair, start with checking these safety switches before considering
a small engine repair shop.
From this point,
small engine repair is like any other
auto repair. Any engine including small engines require
three things to start. They require air and fuel to burn, and they need a spark to ignite the fuel.
If your small engine don't start, begin by removing the spark-plug and confirming it fires by allowing it to rest against the
engine and cranking a few times. A weak spark may not be able to burn the fuel, and is caused by having a bad spark-plug,
the wrong gap, a weak battery, or weak coil or plug wire. Don't assume no-spark is the plug. It can be a fuse or safety switch,
loose ground wire, key switch, solenoid, battery, coil, or plug wire. With an electric start, many of these can be ruled out quickly.
If the electric starter works, ground is good, battery is good, and likely fuses are good (at least for small engines). On pull start,
there is no battery (or key generally) and often no fuses, but there may be
safety switches for oil, brake/clutch, or a seat/handle
switch or lever to prevent starting if not in proper use. Check these, and if all is good, replace your sparkplug to complete your
small engine repair.
When spark is good, but the small engine won't start, check your air flow. An obstruction in the air intake or a
clogged air filter
will choke the small engine and prevent the fuel from burning. For this small engine repair, remove your air filter and inspect
the air intake at the carburetor for obstructions. This includes the choke flap. If the small engine cannot get air because of the
choke engaged, it may start briefly and die due to lack of air to fuel. If your small engine starts with the air filter removed,
you need to clean or replace the air filter to perform your
small engine repair.
If your small engine don't start after checking your air filter and intake for obstructions and you are getting spark to the cylinder,
you likely have no fuel causing your small engine repair. Start by confirming fuel in the gas tank and that if your system has a
fuel shut-off valve be sure it is open. Then, pull the fuel line loose
by the carburetor. If no fuel is running out, there is an obstruction in the fuel tank, fuel line, or fuel filter. You can check
the tank by shaking it to see if fuel begins to flow, and if your fuel filter is
accessible, remove the fuel line from the tank side
of the filter to check for fuel. If fuel begins to run, or if the fuel filter is in the tank, you likely need to replace the fuel
filter to repair your small engine.
If fuel begins to run when you removed the fuel line from the carburetor, you will need to remove the
carburetor for cleaning to
repair the small engine and get it running again. Cleaning a carburetor is not as hard as you may think. With the air filter off,
there are only a few bolts that hold the rest of the air intake and
carburetor onto the small engine. Finish removing the carburetor
and unhook the springs, throttle, and choke cables as needed.
Now, to begin cleaning the
carburetor, unscrew the drain screw at the
bottom or lower side of the carburetor to open the drain passage, and allow the fuel to drain. Then, remove the bolt from the bottom
of the carburetor to remove the bottom pan and open the carburetor. There will be a gasket or rubber ring between these pieces. Don't
lose it and inspect it for replacement as needed.
Attached to the stem inside of the
carburetor will be a float with a slip pin at the
back, and may have some other pieces. Among them is a needle valve that
attaches to the float and goes into a whole. This is what
allows the fuel to flow into the carburetor bowl. Be very careful with these parts and to put them back correctly. If you
need, take a picture.
Now, check your float for leaks or fuel inside of the float. If damaged, replace the float and move on. Next, you
need to clean any glue like gummy buildup off of the needle, float, and other parts, and clean out the various passages. Many of these
are in the stem. To clean them, you will need to remove the screw at the bottom of the stem that goes inside. You will need to
blow through the passages to confirm they are clear of obstructions, and then replace the screw at the bottom of the stem, and replace
the needle valve and float. Be sure to clean the hole where the valve goes. This is often the clog that stopped fuel flow.
Re-install
the gasket/ring and bottom pan, and snug the bottom bolt, but don't close the drain port screw. You will want to confirm flow of fuel
through the carburetor before re-installing the carburetor. This is done by attaching the fuel line and confirming it flows out the drain
port. If fuel is not draining through, repeat the process and confirm correct assembly, and if fuel flows through the
carburetor,
close the drain port screw and re-install the carburetor and air intake. This should complete your small engine repair and have your
small engine running again.
Note: If your small engine has a fuel pump or primer bulb, you will need to check it before rebuilding the carburetor. Primer
bulbs deteriorate and leak allowing air to suck in instead of fuel.
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