On gasoline trimmers, both two-stroke internal combustion engines (ICE) and four-stroke engines are used. But the ignition system in them is no different from each other, so the repair and tuning of this ignition system will be the same for different types of internal combustion engines.
How does the ignition system on the trimmer work?
The two-stroke engine ignition system consists of 2 elements: a flywheel and a coil (magneto). The figure below shows how they look.
On the flywheel is the impeller, which works as a fan to cool the engine. Also on one side of the wheel are permanent magnets, the figure shows the arrow.
During the rotation of the flywheel in the coil, an electric current is produced, which serves to produce a spark on the spark plug. A spark appears at the moment when the magnets are directly under the magneto.
Why do I need to adjust the ignition?
In some cases, when the engine does not start, an ignition adjustment will be required. Of course, you first need to check the serviceability of the spark plug and high-voltage cable with a cap.
Ignition control on a two-stroke engine is necessary 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 candle should appear at the moment of compression of the fuel by the piston when it does not reach the top dead center (TDC) just a little. When the piston passes TDC, the fuel mixture ignites, causing the piston to fall under the action of the energy of the explosion.
Therefore, if for any reason (mainly due to the displacement of the flywheel on the shaft relative to its initial position), the fuel ignites before the piston passes the TDC, it returns, and the crankshaft rotates in the opposite direction. Such a movement can damage the starter assembly, tear the launch cord, etc. In this case happens early ignition of fuel.
May also be late ignition on the trimmer: the piston after compression of the fuel, which is not ignited, goes down, and at this moment a spark appears. In this case, the engine will either not start, nor it will significantly lose power, and it will be bad to gain momentum.
But such problems with early or late ignition on two-stroke ICEs 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. Besides, the wheel is fixed to the shaft with a key and nut. Therefore, incorrect installation of the part is excluded.
The ignition control is to set the correct gap between the magneto and the flywheel.
How to check the serviceability of magneto?
Magneto is the main component in the engine ignition system and is a coil with primary and secondary windings located around the core. Often, due to a malfunctioning magneto, the spark on the spark plug disappears, and the ignition of the fuel does not occur.
To check the coil, you will need to use a tester and perform the following steps.
- On the tester, going into the resistance measurement mode, you need to set 200 Ohms. This method will check the primary winding.
- Connect one electrode of the tester to the “mass” of the coil, and the second 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 will need to set the instrument switch to 20 com. Further, one probe of the device is inserted into the cap of the candle, and the second is connected to the “mass”. Normally, resistances should be in the range of 4-6 lump or higher (depending on the model).
When the circuit is open, the device will show infinity, and when it is closed, it will show 0 (zero).
If you do not have a tester, you can use the following method, taking great care so that the electrode does not touch the cylinder. Otherwise, the coil will blow.
- Remove the cap from the candle. Candle twist does not need to save compression.
- It is necessary to insert a nail without a cap into the cap. The nail must be of such diameter that it is well kept in the cap.
- Tie the cap with a nail to the cylinder using a dielectric, so that the gap between the electrode and the cylinder body is in the range of 5.5 to 7 mm (but in no case does not touch the “mass”).
- Use the starter to imitate the engine start several times. The ignition button must be on.
- Observe whether a spark appears and what color it has.
Normally, the spark should be strong, white, or have a bluish tint. If the spark is weak and its color is orange or yellow, this indicates a faulty magneto.
You should also take into account the fact that sometimes a magneto in a frozen state can produce a good spark. But after heating due to internal faults ceases to produce current. As soon as the coil cools down, the trimmer starts up again and works for a while until the magneto warms up again. This coil must be replaced.
Sometimes a spark plug can cause a similar problem with the heating, even if the coil is healthy, so you need to check both parts.
Ignition Adjustment Algorithm.
Trimmer lighting is fairly easy to adjust.
- Remove the cover from the engine by unscrewing all the bolts holding it. For example, on the Patriot trimmer PT 2540, to remove the cover, you need to unscrew the air filter housing and remove it from the latches with a flat screwdriver.
- After that, the plastic case can be easily removed. Using a screwdriver, loosen the two bolts (do not completely unscrew) holding the magneto.
- Turn the handwheel so that the magnets are on top.
- Further, to correctly set the best gap between the flywheel and the coil, you can use the usual business card or pocket calendar. If you do not have one or the other, you can use an A4 sheet of paper to adjust the ignition by folding it two times (as a result, you will have a thickness of 4 sheets). This thickness will be enough to get the optimum clearance and adjust the ignition. Insert a business card or paper between the coil and the magnets.
- The magnetic field will attract the coil to the flywheel. Holding the magneto with your fingers in this position, tighten the bolts holding it.
- Remove the card. After that, the ignition on the trimmer will be adjusted.