Owners of popular Chinese motorcycles often face a situation when the engine suddenly loses traction or begins to work unstable. Owners are wondering why the ignition on the Alpha is straying and are looking for ways to quickly get the equipment back on track without a costly visit to the service. The problem is really common, as the engine design is 139FMB Its modifications have their own characteristics that require attention to detail in the maintenance.
Unstable operation of the spark formation system can be caused by a whole range of factors, from banal oxidation of contacts to mechanical displacement of the gas distribution elements. Understanding the physical processes inside the cylinder and electrical circuit allows you to diagnose a malfunction the first time. In this article, we will discuss in detail the mechanical and electrical aspects that affect the moment of ignition of the mixture.
Before you start to complex adjustments, it is necessary to exclude the simplest causes that are often ignored. Breaching of the seal a crankcase pallet or weakening of the stator attachment can cause the sensor to shift. It is also worth checking the condition of the wiring, as the vibrations characteristic of light motorcycles gradually destroy the connections.
Mechanical causes of phase displacement and gaps
One of the most common reasons why the moment of spark formation “floats away” is a violation of the regulation of the thermal gap of the valves. If the gap on the intake or exhaust valve becomes too small or disappears altogether, the compression falls and the engine behaves as if the ignition is shot down. In motors like 139FMB and 152FMI This parameter is critical for stable operation at all speeds.
Gas distribution mechanism (GRM) chain stretching is a natural wear process that directly affects phases. When the chain is pulled, the marks on the asterisk of the camshaft cease to coincide with the risk on the crankcase at the upper dead point (BMT). This leads to the fact that the spark skips at the wrong moment when the piston is in the right position.
⚠️ Note: When replacing the HRM chain, be sure to use a new guide (sedative), since the old one may have a production that will accelerate the wear of the new component.
The luft shaft of the generator or weakening of the bolt of the rotor attachment can also cause a failure. If the magneto rotor has a free stroke relative to the crankshaft, the position of the Hall sensor or induction coil changes chaotically. This creates a floating ignition effect that cannot be eliminated by simple adjustment.
To diagnose the mechanical part, you will need a set of probes and keys. It is necessary to remove the valve cover and turn the crankshaft to combine the marks. Then the gap between the kernel and the end of the valve is checked with a probe. Normal values are usually 0.05 mm for inlet 0.05 mm for release on a cold engine, but accurate data is better to look in the manual for a particular model Alfa.
Electrical faults of the ignition system
If the mechanics are fine, the problem is the electrician. A switch (CDI) is the “brain” of an ignition system that forms a spark. Over time, internal electronics can degrade, especially if the motorcycle is operated in high humidity or vibration conditions. Unstable operation of the switch often manifests as ignition misses under load.
The ignition coil and high-voltage wire are the weak link in budget motor vehicles. A breakdown in the insulation of the wire or a crack in the candle cap leads to a voltage leak. In wet weather, the spark can go to the mass, without reaching the candle, which is perceived by the driver as a shot down ignition. Visual inspection in the dark with the engine running helps to identify such “tracks” of current leakage.
- 🔌 Oxidation of contacts: connectors under the tank are often oxidized, increasing the resistance of the chain and weakening the spark.
- 🕯️ Ignition candle: the incorrect calyl number or the breakdown of the insulator candle directly affect the moment and power of the spark.
- 🧲 Hall's sensor.In electronic systems, a failure in the operation of the crankshaft position sensor gives an incorrect signal to the switch.
It is important to check the battery charge. Although the ignition system on many Alphas is powered by a generator (AC), the low voltage in the onboard network can affect the operation of additional equipment and the stability of the spark at low revs. Use a multimeter to check the voltage at the terminals with the engine running.
How to check the ignition coil with a multimeter?
To check the coil, you need to switch the multimeter to the resistance measurement mode (Oms). Measure the resistance of the primary winding (between the low voltage terminals) and the secondary (between the central terminal and the housing). The resistance of the primary winding is usually 0.1-0.5 Ohms, and the secondary - 2-10 kOhms. If the device shows infinity or zero, the coil should be replaced.
The impact of the quality of the fuel mixture on the engine
Often drivers look for the cause in the ignition, when the problem lies in improper mixing. If the mixture is too poor (lots of air, not enough gasoline), the combustion rate drops and the engine overheats. This can mimic the symptoms of early ignition. Conversely, a rich mixture burns more slowly, requiring an earlier spark to burn efficiently.
Suction of foreign air through the gasket of the intake manifold is a classic problem. Microcracks in the rubber pipe between the carburetor and the engine lead to the fact that unaccounted air enters the cylinder. The mixture is impoverished, idle turns float, and with a sharp opening of the throttle, you can hear "sneezes" in the carburetor.
To adjust the carburetor PZ19 or Keihin It is necessary to understand the principle of the work of chiclairs. The main jikler is responsible for working at full speeds, and the idle jikler is responsible for low speeds. Incorrect adjustment of the screw quality of the mixture can create the illusion of problems with the angle of ignition advance.
☑️ Diagnostics of the fuel system
Pay attention to the octane number of gasoline used. Air-cooled engines mounted on the Alphas are sensitive to detonation. The use of low-octane fuel causes premature ignition of the mixture, which destroys the piston group and shifts the effective ignition moment.
Diagnosis: How to determine the exact cause
Professional diagnosis begins with an external examination and survey of the owner. It is important to know after what events the problems began: was the wash under pressure, whether the motorcycle got into a puddle, or was the engine repaired? These details help narrow the search.
Using a strobe is the most reliable way to check the angle of ignition advance on a working engine. The device is connected to a high-voltage wire, and flashes of light illuminate the tags on the flywheel. If the label "dances" or does not coincide with the risk on the crankcase in a given range of revolutions, then the ignition is really knocked down or the advance mechanism is defective.
| Symptoms. | Probable cause | Method of verification |
|---|---|---|
| Knocking during acceleration (detonation) | Ignition too early | Strobe scan, fuel octane check |
| Clapping to the muffler | Late ignition / Rich mixture | Adjustment of the carburetor, check of the HRM |
| Tough launch | Weak spark / No compression | Compression measurement, visual inspection of the candle |
| Gas-pressing failures | Air suction / Clogged with a jikler | Carburettor spill, inlet check |
If there is no strobe, you can use the method of "contrary". Put the ignition on the labels perfectly accurately, check the gaps of the valves. If the problem is not gone, look for the electrician or fuel system. Consistent elimination of factors is the key to success.
Ignition adjustment and GRM labelling
The process of ignition on Alfa motorcycles requires accuracy and cleanliness. First, you need to provide access to the generator by removing the right engine cover. Clean the area around the magneto of oil and dirt to see the risks well.
Rotate the crankshaft (usually with a 17mm key per generator bolt or spinning the rear wheel in gear) until the tag is ticked. "T" The rotor won't match the slot on the crankcase. This position corresponds to the upper dead point (IMT) of the compression stroke. It is important to make sure that the piston is compressing rather than pushing the gases out (both valves are closed).
⚠️ Note: Do not confuse the T (Top Dead Center) label with the F (Fire/Ignition) label. Only the "T" label at the time of compression is used to set the GRM phases.
If the marks on the asterisk camshaft do not coincide with the plane of the cylinder head when the "T" label is displayed on the crankshaft, then the GRM chain is stretched or jumped. In this case, it is necessary to loosen the tensioner of the chain, remove the asterisk and reinstall it on the marks, observing the tension of the chain.
For electronically advanced (CDI) systems, physical angle adjustment is not required if the Hall sensor and stator are installed correctly. However, if the stator has oval mounting holes, it can be shifted slightly to adjust the angle, but this is only done with a strobescope and understanding the process.
Prevention and maintenance of the system
That the question "why the ignition on the Alpha" has ceased to bother you, you need to regularly carry out maintenance. Vibration is the main enemy of fasteners. Once a season, hold out the bolts of the engine, generator and valve cover. Use a thread fixator for responsible connections.
Protection from moisture is the second important aspect. Treat the connectors of the electric circuit with a special lubricant for contacts. This will prevent oxidation and signal loss. Also monitor the condition of the air filter: a clogged filter violates the mixture, which indirectly affects the operation of the ignition.
- 🛢️ Oil replacement: oil replacement keeps the GRM chain tensioner in working condition.
- 🔧 Pimp: Control the tightening of the HBC bolts and the valve cover.
- 🧹 Cleanliness: Engine washing should be done carefully, without direct pressure of water on the electrician.
Timely replacement of consumables, such as spark plugs and air filters, is cheaper than repairing the engine after detonation or working on a poor mixture. Remember that the life of Chinese engines depends on the quality of the lubricants and fuel used.
Regular inspection of valve heat gaps and the condition of the HRM chain prevents 90% of the problems associated with “downed” ignition on Alfa motorcycles.
Frequently Asked Questions (FAQ)
Can I ride a motorcycle if the ignition is knocked down?
It's highly discouraged. Riding with improperly exposed ignition leads to engine overheating, valve burnout and destruction of the piston group due to detonation. This can cause costly overhauls.
How often should I change the chain to Alpha 110?
The resource of the chain depends on the quality of the oil and the style of riding. On average, replacement is made every 10-15 thousand kilometers. However, if there is a metal ringing to the right of the engine or floating revolutions, check the condition of the chain should be carried out immediately.
Why did the bike get worse after the switch was replaced?
It is possible that an incompatible switch is installed. On Alfa motorcycles there are models with speed limit (strangers) and without. Also, switches can differ in the angle of ignition ahead. Check the conformity of the labels and the number of contacts.
Does a discharged battery affect the spark?
On magneto (AC) ignition systems, the battery has practically no effect on the spark power when the engine is running. However, if the battery-powered (DC) system is running or the electronic starter is spinning poorly, creating low revs, spark formation can be unstable.