How to check the ignition on a petrol cutter

Insufficient sparking

The weak spark on the magneto is caused by a damaged capacitor. To eliminate the breakdown, it is necessary to replace the failed part.

Method 2

Magneto diagnostics using a multimeter is a solution that can be implemented on your own with such a measuring device. In this case, it is necessary to do the following.

  • Switch on resistance mode on the Meter and set to 200 ohms to test the primary winding.
  • Connect multimeter electrodes to magneto ground and output terminal. If the winding is intact, the resistance will vary from 0.4 to 2 ohms.
  • Switch on the 20 kΩ tester to perform a secondary diagnosis. In this case, the first probe is connected to the “mass”, and the second is installed in the spark plug cap. Normal values ​​are at least 4-6 com. If the circuit is damaged, then the tester will show infinity, and in case of a short circuit. zero.

For exact details of what the tester should read when checking primary and secondary winding, see the grass trimmer instructions for use.

Replacing breaker contacts

After disassembling the magneto, it is necessary to remove the old breaker contacts and install the new ones correctly. To accomplish this, you must:

  • move the latch, remove the cover from the breaker;
  • unscrew the screw holding the connecting wire;
  • remove the screw securing the breaker plate to the magneto cover and remove it;
  • get the screw securing the breaker spring;
  • remove the lock washer from the axle, and then the lever with the cushion assembly, which it holds;
  • unscrew the screw securing the contact post, remove the part from the axle.

Assemble the assembly with new contacts in the reverse order.

On a note! Despite the ease of operation, most often trimmer owners prefer to simply replace the magneto with a new one.

Magneto. design and operating principle

The purpose of the ignition coil is to convert the rotational energy into a high-voltage discharge and form a spark that ignites the fuel mixture. In an internal combustion engine, this part is called a magneto, since in it an alternating current is generated from the rotation of a permanent magnetic rotor or armature.

check, ignition, petrol, cutter

Magneto structurally consists of two windings: high and low voltage. A capacitor with breaker contacts is connected in parallel to the latter. Whereas the leads of the high voltage winding are connected to the candle and the body. They are both wound on a core, between the poles of which a rotating magnet is installed, magnetized longitudinally.

On a note! The whole structure looks like a large coil mounted on a U-shaped core.

Unstable sparking

If the magneto sparks intermittently, the contacts must be checked first. They could be burnt or oily. The carbon deposits found are cleaned with a file, and the oil is wiped off with suede, previously soaked in gasoline. The second possible cause of the problem is the adjustment of the gap between the contacts. To eliminate it, you need to set the correct distance.

If the spark is intermittent, it could also mean that the breaker arm pad is worn out. To eliminate the malfunction, you must change the lever to a new one. In addition, the clearance should be adjusted, as with another possible cause of breakdown. misalignment of the outline.

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Capacitor breakdown can also be the culprit for interruptions in spark formation. In such a situation, replacement of the damaged part is required, since it cannot be repaired and recharged.

Problem prevention

Often, breakdowns of the ignition coils are associated with a short circuit or breakage of the windings and mechanical damage to the magneto case. This is due to strong shocks, liquid ingress and oxidation, and overheating. If such incidents are avoided, there is no need to worry about the integrity of the ignition coil.

Important! To prevent regular failure of the spark plugs. one of the most important components of the ignition system. you need to fill up with high-quality fuel. Bad fuel spoils these parts.

One of the magneto assemblies that regularly suffer from use are the high voltage wires through which the spark plugs receive current from the ignition module. They have a long service life, but they are damaged by the users themselves by careless handling when replacing candles, inadvertently pulling on the wire itself, and not on the tip. Another problem that can happen to them is moisture ingress and oxidation or damage to the insulation. By carefully pulling out the spark plug and avoiding liquid penetration into the instrument, these problems can be avoided.

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So, the repair of the ignition coil is not very difficult and can be carried out by the user independently, but subject to the above procedure for disassembling and replacing the magneto or breaker contacts.

Typical problems. causes

The malfunctions that most often occur with magneto are typical for trimmers from different manufacturers. As a rule, this is a weak spark or its absence, as well as the presence of interruptions in this process.

Replacing the magneto

Advice! Another good solution would be to provide an old ignition coil so that the seller can pick up a new part.

To remove the magneto, remove the plastic cover from the grass trimmer. This process is different on different brushcutter models. It is usually necessary to remove the bolts, but on some gas trimmers it may be necessary to depress the latches. After that, access to the coil is opened. To remove the part, you need to unscrew the retaining fasteners and disconnect the wires.

When installing a new part, you need to correctly set the distance between the flywheel and the magneto. To do this, turn the flywheel upwards with the magnets, install the coil and secure it, but do not fully tighten the screws so that there is a small distance between the parts. Next, between the coil and the flywheel, you need to put a calendar, a business card or a A4 paper sheet folded in four, you can also use a plastic strip cut from a bottle. These tweaks will ensure adequate clearance between the flywheel and the magneto. A more competent solution would be to use a special template, but purchasing it for the sake of once is impractical. Next, you need to tighten the fasteners, remove the object between the parts, and, holding the magneto with your hands so that it does not spin, tighten the fixing screws tightly. After that, you should turn the flywheel and make sure that it does not catch the coil anywhere. Now you need to connect the wires and insert the candle into the cap, and then check the operation of the device.

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How the trimmer ignition system works

The ignition system of a two-stroke internal combustion engine consists of 2 elements: a flywheel and a coil (magneto). The picture below shows how they look.

The flywheel has an impeller that acts as a fan to cool the engine. Also on one side of the flywheel are permanent magnets, shown in the figure by an arrow.

When the flywheel rotates, an electric current is generated in the coil, which serves to produce a spark on the spark plug. A spark appears when the magnets are directly below the magneto.

How to check the health of a magneto

Magneto is the main part of 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 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 lead 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 device switch to 20 ohms. 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 from 4-6 kOhm and above (depending on the model).

When the circuit is open, the device will show infinity, and when closed. 0 (zero).

If you do not 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. You do not need to unscrew the candle in order 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.
  • Tie the cap with the nail 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 in no case touches the “mass”).
  • Using the starter, simulate the 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. 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 malfunctions, it ceases to produce current. As soon as the coil cools down, the grass trimmer starts up again and runs for a while until the magneto warms up again. This coil needs to be replaced.

Ignition Coil Primary & Secondary Resistance Testing

Sometimes a spark plug can cause a similar heating problem even if the coil is OK, so both parts need to be checked.

Trimmer ignition setting

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, therefore, the repair and adjustment of this fuel ignition system will be the same for different types of internal combustion engines.

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Why do I need ignition adjustment

In some cases, when the engine does not start, the ignition will need to be adjusted. Of course, first you need to check the condition of the candle 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 spark 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 original 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, early ignition of the fuel occurs.

There may also be a 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 bad 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.

Basically, ignition adjustment is about setting the correct gap between the magneto and the flywheel.

Ignition adjustment algorithm

Trimmer ignition is quite simple to adjust.

    Remove the engine cover from the engine by unscrewing all the bolts holding it. For example, on a Patriot (Patriot) PT 2540 petrol cutter, to remove the cover, you will 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, unscrew the 2 screws (not completely unscrewed) holding the magneto.
  • Turn the handwheel so the magnets are at the top.
  • Further, in order to correctly set the best clearance between the flywheel and the coil, you can use a regular business card or calendar. If you do not have either one or the other at hand, then to adjust the ignition, you can use a sheet of A4 paper by folding it 2 times (as a result, you will get a thickness of 4 sheets). This thickness will be sufficient to obtain the optimal clearance and adjust the ignition. Insert a business card or paper between the spool and the magnets.
  • The magnetic field will pull the coil towards the flywheel. While holding the magneto in this position with your fingers, tighten the bolts that hold it.
  • Remove the business card. After that, the ignition on the trimmer will be adjusted.