Diagnostics of magneto
Magneto is a key component in engine ignition systems. It is a cored coil that is surrounded by a primary and then a secondary winding. If this part is defective, there is no spark from the spark plug and the fuel will not ignite.
If you cannot use a tester, there is another way to test. In this case, it is important not to touch the cylinder with the electrode, otherwise the coil will be damaged.
- Remove the spark plug cap. The plug should not be unscrewed, as this will maintain compression.
- Then you need to pick up the nail with the cap removed and insert it tightly into the cap.
- Next, the cap with the nail should be securely tied to the cylinder with a dielectric. In this case, the electrode should be at a distance of 5.5-7 mm from the cylinder body, but not touch the mass.
- Then, using the starter, you need to simulate starting the engine with the ignition button turned on. In this case, you need to carefully monitor whether a spark appears, and try to determine its color.
There is one important point to consider when diagnosing: unheated magneto in any state can form a powerful spark. However if it is faulty, then, after warming up, it stops creating a current, and the trimmer won’t start. Later, after cooling down, the coil returns to the operating level, the tiller turns on and runs for a while at idle or under load, until the temperature of the magneto rises again. In this case, the part must be replaced with a new one.
Trimmer ignition. Principle of operation and possible malfunctions
If the owner of the lawn mower wants to adjust the ignition system on his own, he should understand the principle of operation of this unit. In an internal combustion engine, it consists of a flywheel and a magneto (coil). In turn, the flywheel includes an impeller that performs the function of cooling the motor and a number of permanent magnets.
Trimmer ignition setting
Gasoline trimmers use both two-stroke internal combustion engines (ICEs) and four-stroke ones. But the ignition system in them is no different from each other, therefore, the repair and adjustment of this fuel ignition system will be the same for different types of internal combustion engines.
Why do I need ignition adjustment
In some cases, when the engine does not start, ignition adjustment will be required. Of course, first you need to check the condition of the plug and the high-voltage cable with a cap.
It is necessary to adjust the ignition on a two-stroke engine in order to ensure timely ignition of the fuel in the engine combustion chamber. Below is a diagram from which you can understand the principle of operation of the internal combustion engine.
The spark in the plug should appear at the moment the fuel is compressed by the piston, when it does not even reach the top dead center (TDC). When the piston passes TDC, the fuel mixture ignites, as a result of which the piston goes down under the action of the explosion energy.
Therefore, if for some reason (mainly due to the displacement of the flywheel on the shaft relative to its initial position), the fuel ignites before the piston passes TDC, then it goes back, and the crankshaft rotates in the opposite direction. This movement can damage the starter assembly, cut the starter cord, etc. In this case, there is early ignition of fuel.
It can also be late ignition on the trim: the piston, after compression of the fuel that has not ignited, goes down, and at this moment a spark appears. In this case, the engine will either not start, or it will significantly lose power and it will be difficult to gain speed.
But such problems with early or late ignition on two-stroke internal combustion engines are quite rare, since the flywheel with magnets is already installed in the correct position, which is perfectly synchronized with the movement of the piston. In addition, the flywheel is secured to the shaft with a key and nut. Therefore, incorrect installation of the part is excluded.
How to check the health of a magneto
Magneto is the main part in the engine ignition system and is a coil with primary and secondary windings located around the core. Often, due to a malfunction of the magneto, the spark on the spark plug disappears and the fuel does not ignite. To check the coil, you will need to use a tester and follow these steps.
- On the tester, after switching to the resistance measurement mode, you need to set 200 ohms. In this way, the primary winding will be checked.
- Connect one electrode of the tester to coil ground and the other to the contact coming out of the magneto. Normally, the resistance should be between 0.4 and 2 ohms.
- To check the secondary winding, you need to set the device switch to 20 kΩ. Further, one probe of the device is inserted into the candle cap, and the second is connected to the “mass”. Normally, resistance indicators should be in the range of 4-6 kΩ and above (depending on the model).
If you don’t have a tester, then you can use the following method, being very careful so that the electrode does not touch the cylinder, otherwise the coil will burn out.
- Remove the cap from the candle. The candle does not need to be twisted to maintain compression.
- It is necessary to insert a nail without a cap into the cap. The nail should be of such a diameter that it adheres well to the cap.
- Attach the nail cap to the cylinder using a dielectric so that the gap between the electrode and the cylinder body is between 5.5 and 7 mm (but never touches the “ground”).
- Using the starter, simulate engine start several times. The ignition button must be on.
- Observe if a spark appears and what color it has.
Normally, the spark should be strong, white or bluish in color. If the spark is weak, and its color is orange or yellow, this indicates a faulty magneto.
You should also consider the fact that sometimes cold magneto can give a good spark. But after heating, due to internal faults, it ceases to produce current. As soon as the coil cools down, the trimmer starts again and runs for a while until the magneto warms up again. This coil must be replaced.