Very often on various forums people ask questions like “Why does my moped stall and won’t start?”, and often receive a bunch of advice on what needs to be replaced, even advice to change the moped to a “cooler” one. In fact, even a technically untrained person can diagnose the main engine malfunctions. Let's sort it out in order.
So, for stable operation of the engine, three conditions are needed:
- A good spark on the spark plug electrodes, at the right moment.
- The presence of the “correct” working mixture in the combustion chamber.
- The presence of “compression”, that is, a working cylinder-piston pair and properly functioning valves.
You don't need to be an experienced mechanic or have a bunch of expensive tools to diagnose your moped. Let's look at simple methods for finding a fault.
Visual inspection
You should always check using the “from simple to complex” . If the moped was working like a clock just yesterday, but today it refuses to start, remember what happened to it during this period of time. Maybe you made changes to the electrical circuit, or adjusted the carburetor, or washed the moped, or did some other work - sometimes this helps to localize the fault. If possible, return everything back.
Before starting the test, carefully inspect the moped. You may notice a torn or exposed wire or some other small thing. Sometimes this helps a lot.
Checking the presence of a spark and the condition of the spark plug
This is the simplest check that every moped owner can carry out, having only a spark plug wrench or a spare spark plug on hand. Moreover, if you unscrew the spark plug from the engine, you can at the same time assess its condition and understand by the color of the carbon deposits how correct the working mixture is being prepared by the carburetor.
So, if you unscrew the spark plug from the engine, pay attention to the carbon deposits that cover the central electrode. The carbon deposits should be brown or light brown in color. If the carbon deposits are black, this indicates that the mixture is too rich, or the spark plug is faulty, or the engine is “eating” oil. Perhaps this is the reason for poor engine performance.
Also pay attention to the presence of liquid on the candle. If the spark plug is “wet”, that is, there is gasoline on the spark plug, then gasoline still enters the combustion chamber, but does not ignite. There are at least three reasons why a spark plug may be wet:
- trying to start the engine with the ignition turned off - if you turn the engine with the kick starter for a long time, the spark plug will simply flood with fuel and it will not be able to work normally. To solve the problem, the candle needs to be dried, for example, heated with a lighter.
- The spark plug is faulty - if the spark plug insulation is broken or the gap is broken, the spark plug will not work normally. Only replacing the spark plug with a known good one will help here.
- ignition system faulty
Now we put the tip on the spark plug and press it to a metal surface, for example, to the engine head, turn on the ignition and turn the engine with the kickstarter. It is more convenient to check the spark together, so that one person holds the spark plug and the other turns the engine. But in principle, one person can handle it. Be careful - there is high voltage at the center electrode of the spark plug.
If there is no spark, then the ignition system is at fault. Check all wires for breaks or shorts to ground. All electrical wiring connectors must be connected. If possible, replace the ignition coil with a known good one. Check if the generator coils are damaged. You can read more in the article “The moped has lost its spark, what should I do?”
If you can’t figure out the wiring, contact someone who knows how to do it.
If there is a spark, then most likely the problem is in the power system. Screw the candle into place and continue.
What to do if the Alpha moped does not start, causes of failure
Anyone who has purchased their first moped rarely thinks about the rules of its operation, maintenance and possible repairs. As a result, parts wear out faster, the moped constantly breaks down and works intermittently.
While the moped is relatively new, problems with the power unit and chassis system are almost invisible. But every day of driving a vehicle, with such an attitude towards it, adds to the likelihood that the moped will break down.
Unfortunately, it happens that young people, either due to lack of experience or because of their frivolity, do nothing if the vehicle is “jamming” and ride it until the moped stops starting.
Do you want to know why a Minsk motorcycle won’t start? All possible breakdowns.
Is there anything that can be done if the moped does not start from the starter? There are many reasons that lead to this. If the reason is serious, then it’s better to turn to experienced mechanics. Well, minor breakdowns are easy to fix yourself. Fortunately, mopeds produced in the USSR are distinguished by their simplicity of design, which also helps with tuning. For example, you can tune a moped yourself without any problems with a minimum of tools in the garage. Of course, you could use the help of an experienced mechanic, but for a novice motorbike enthusiast it is enough to be attentive and ingenious.
Electrical problems
There is only one symptom of a wiring problem - the moped will not start from the starter. To check that this is not possible, you need to turn on the rotation in “ON” mode. The rotation does not work - something happened to the wiring.
To fix the problem, you need to look at the battery terminals to find out if the wires themselves are damaged. If everything is fine with the wires and terminals, then the problem is insufficient battery charge. In order for the battery to work, its charge must reach 13 volts.
When the charge is not much less (about 9-12 volts), try starting the moped from the kickstarter, so you can ride the bike for about fifty kilometers. If everything is fine with the battery, but the moped still won’t start, you need to contact a service station, because you won’t be able to do it yourself.
Poor fuel level
This problem can be seen by the fact that the moped can be started, but it “coughs” and stalls. To fix the problem, you need to add gasoline to the system. This can be done by adjusting the suction.
Also try changing the amount of fuel mixture entering the carburetor. To do this, you need to find a small bolt on the carburetor, and use a screwdriver to calibrate it.
Carburetor clogged
The symptoms of the problem are the same as in the previous case - you can start the moped, but then it stalls. That is, there is a spark, there is gasoline, but the moped does not start. In order to check whether the carburetor has broken down, you need to check how gasoline flows from it into the cylinder.
Take the spark plugs and wet their contacts with gasoline. Then screw the spark plug being tested into the cylinder and try to start the moped. If the bike starts this way, it means the carburetor will have to be repaired.
If you are on the road and need to quickly get to your destination, you can clean the supply hoses by blowing them with a pump. If this does not work, then you need to completely clean the carburetor.
To check if this is the case, you need to remove the cover and carefully check the filter. Most often, foam rubber is used as a filter. Even a quick check is enough for you to figure out whether the filter is working. The filter needs to be replaced if it is covered in oil or crumbles when touched.
The spark plug is not working properly
The moped will not start if the spark plugs are faulty. To diagnose this, you need to check the spark plug and the area under it. The place under the candle should be completely dry. A wet spark plug means there is too much gasoline in the fuel mixture. If something is wrong, the area under the candle needs to be wiped dry.
Very often, starting the engine is prevented by carbon deposits on the spark plug, which prevents it from producing a spark. Using a spark plug, you need to unscrew the spark plug and check it. It's very simple. To check if the spark plug will work, you need to put a cap on it and touch its bottom to the frame of the bike.
Then you need to try to start the bike using the kickstarter. If there is no spark, it means that the contacts in the spark plug cap are not functioning. Then the contacts are “pressed”. And if a spark does not appear even after this, the spark plug needs to be changed.
Often the moped does not start due to debris getting into the fuel pump or fuel pipes:
- tubes (to check this, remove the tube supplying gasoline from the fuel tank. Then blow it out. Then, drain all the fuel from the tank and refill the moped);
- fuel pump (if the fuel pump is broken, remove the two remaining tubes and blow out the lower hole. If fuel does not come from the upper tube, then the fuel pump is indeed broken).
The muffler is broken
It happens that the moped cannot be started due to a faulty muffler. To detect a breakdown, you need to put your hand on the muffler with the moped engine running. If you don't feel anything, then the muffler is clogged. And then you will have to go to a service station for repairs.
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Checking the engine power system
First of all, you need to make sure that there is enough gasoline in the gas tank. There is a small tube inside the gas tank that takes gasoline not from the bottom of the gas tank, but a little higher. Therefore, it may turn out that there is still gasoline in the tank, but it does not flow into the carburetor. Therefore, if possible, add gasoline to at least half the tank and try to start the moped again. Perhaps this is the reason.
You also need to know that the gas tap of the Alpha moped has two positions: in one, it takes gasoline closer to the bottom of the gas tank, and in the other, a little higher. If you don’t know in which position the gas tap is open, try installing it in a different position, maybe this will help.
It is very convenient to check the gasoline supply if you have a transparent tube from the gas tank to the carburetor, or have a replaceable gas filter installed. In this case, you can immediately see whether there is gasoline or not.
There is also another simple check of the power system: take a small amount (5-10 ml) of gasoline into a syringe, remove the air intake tube from the carburetor and pour gasoline directly into the carburetor. If after this the moped starts up, or as they say “catch,” then the reason is definitely in the gasoline supply and you need to check the fuel supply and carburetor.
If after all the described checks the problem is not found, there is one more check left - checking the engine compression.
Switch
To check the switch, we need a test lamp - this is a regular 12-volt light bulb with wires routed out for easy connection. A test light and connect one end to the ground wire, the other to the ignition coil wire. We turn the engine with the starter.
If the light comes on, the switch and its wiring are working properly. If the light does not light, then the switch or switch wiring is faulty. In order to be 100% sure that the problem is not with the switch, I recommend replacing it with a known good one. A switch for Chinese mopeds is inexpensive, if it suddenly turns out that the old switch is working, let it remain in “stock” until the next check.
We measure compression
Compression is the pressure in the cylinder at the end of the compression stroke. The magnitude of this pressure allows you to assess the condition of the engine. A working Alpha moped engine should have a compression of at least 8-10 kg/cm² (“atmospheres”) . If it is less, then the engine is faulty: either the piston rings are worn out or the valves are leaking. Most likely the engine will need to be disassembled.
Compression is measured using a compression meter - a special pressure gauge that is inserted or screwed in (depending on the design) instead of the spark plug.
Before measuring compression, it is advisable to warm up the engine, but if it does not start, you will have to measure it cold. It is also advisable to unscrew the carburetor or open the throttle valve and turn off the fuel supply.
The engine must be rotated using an electric starter or kickstarter until the compression meter readings stop increasing.
When the compression is less than 8 atmospheres , you need to pour 10-15 ml of engine oil into the spark plug hole using a syringe. If after this the compression increases noticeably, it means the piston rings are worn out . If not, then the problem is in the valves or camshaft drive . The most common reason: the camshaft drive chain is broken or has slipped, or the valves are bent/broken.
Ignition coil
And finally, the last, but one of the most important reasons for the lack of a spark, is the ignition coil, or rather its breakdown. With the proper knowledge, you will have to check the functionality of the ignition coil; to do this, you need to connect a low-power light bulb to it, which should check the current supply from the coil.
In most cases, you can fix the lack of a spark yourself; fortunately, the design of mopeds such as Alpha is quite simple, the design is created in such a way that all parts are visible and can be quickly replaced. Also, the cost of spare parts for Alpha mopeds is low, which is a big plus. But if you cannot find the cause of the breakdown yourself, we recommend turning to professionals.
Checking the ignition timing
If there is a spark, fuel is supplied, compression is fine, but the moped still does not start - the ignition timing may be off.
On 139fmb engines, which are installed on alpha, the ignition timing is not adjustable. It is rigidly determined by the position of the flywheel on the crankshaft. The engine crankshaft on the generator side has a conical surface on which the flywheel (also known as the generator rotor) is tightly seated. The correct position of the flywheel is set using a key that is inserted into the crankshaft keyway.
You can check this visually (remove the generator cover, unscrew the nut securing the flywheel and see if the grooves match). But the groove on the crankshaft cannot always be seen (depending on the specific instance), so there is a more reliable way: buy or borrow a strobe light from someone (many car repair shops have one), unscrew the plug on the generator cover and check that flashes occur at the same time the label || appears in the window.
If the moped is not
Sometimes it happens that the moped does not want to start after several hours of inactivity. However, after warming up, it works and starts stably. Let's figure out why this happens.
When the engine is cold, all clearances (in the piston, in the valves, etc.) are far from ideal. Plus, when fuel gets on cold engine parts, it evaporates worse and therefore ignites worse. Because of this, during a cold start the engine needs a richer mixture than usual. It is for this purpose that devices are made on carburetor engines to enrich the mixture at start-up.
On the Alpha moped (and similar ones), an air damper is installed. It reduces the air flow and thereby enriches the working mixture. The damper has two positions: “closed” - the lever is raised up, “open” - the lever is lowered down. When starting “on a cold” air damper must be closed (lift the lever up) . When the engine runs for a while with the throttle closed, it needs to be opened. Driving with the throttle closed will lead to increased fuel consumption and the formation of carbon deposits on the spark plug and piston.
What to do if a cold moped does not start even with the throttle closed? Try using a syringe to fill in 5-7 ml. gasoline directly into the carburetor inlet pipe. If the moped starts after this, then the carburetor needs to be adjusted. If it doesn’t start, check the spark and compression (see above).
Alfa moped won't start
Chinese-made mopeds have different characteristics, but the reasons why they do not start are almost the same. The fact is that Alpha, Delta, Mustang and the like mopeds have similar engine designs and general starting systems, so breakdowns on the Alpha moped can also occur in cases with other models. This article describes what to do if the alpha moped does not start.
In general, scooterists traditionally recommend looking at the serviceability of two main components - the fuel supply and the presence of a spark on the spark plug. Below we will briefly consider each of the reasons.
Checking the spark plug
In the Alpha moped, a completely standard spark plug is installed; a spark is also supplied to it in the traditional way by generating current from a generator. First of all, we check the spark plug for the absence of mechanical damage; it must not only be intact, but there must be no carbon deposits. It is the presence of carbon deposits that in most cases prevents the Alpha moped from starting; the situation can be corrected after cleaning the contacts. This is done with sandpaper, after which the candle becomes beautiful and, most importantly, working.
Next, check for the presence of a spark plug, without removing the spark plug from the spark plug holder, just attach it to a metal surface and try to start the moped from the foot. A spark should form, if not, the reason is in the parts that are responsible for the formation of the spark. In Chinese Alpha mopeds, the ignition coil is considered to be of rather poor quality; even on new mopeds it tends to break.
Presence of compression
A moped like Alpha should produce excellent compression, which can easily be checked as follows: remove the spark plug from the cylinder head and place your finger in the hole, then pull the leg and with good compression, strong pressure should appear until the finger is pushed out. If there is a lack of compression, you will have to remove the engine and the cylinder-piston group itself.
The piston must not hang out in the cylinder and give out compression, and the rings must also be in good condition and fit in size. Otherwise, you will have to change the rings, piston and cylinder. In frequent cases, air in the cylinder is leaked by gaskets that do not create the proper vacuum.
Alpha moped carburetor
A malfunction of the fuel system is a fairly common problem as to why an alpha moped won’t start; you will have to look for the reasons in the carburetor. It is he who is responsible for the correct supply of fuel and its distribution throughout the engine. Often, the carburetors of an Alpha moped tend to become clogged with various debris, and it’s even worse when moisture and water get into the carburetor. Gasoline mixes with water and the CPG is not able to process such a mixture. Remove the carburetor and blow it out well, clean it, adjust the jets and be sure to adjust the position of the needle. This procedure is easy to perform independently.
Battery
If your Alpha moped is well preserved, most likely you know how to start it from the starter. But if you are faced with the impossibility of doing this, and there is no desire to start the Alpha moped from the foot, repairing the electric starter is quite simple. Usually the problem begins precisely because of a dead battery; it is enough to charge it and recheck its functionality.
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