The situation when the scooter 50 cube is not well started on the cold, is familiar to almost every owner of equipment with a 4t engine. This problem is especially acute in the off-season or after a long parking, when the engine cools to ambient temperature. Instead of a confident start, the owner hears only sluggish attempts of the engine to grasp, which often causes irritation and a desire to immediately contact the service.
However, before you panic or spend money on craftsmen, it’s worth understanding the physics of the process. Four-stroke engine requires an accurate balance of fuel-air mixture and spark, which is more difficult to achieve at low temperatures of the cylinder group. Unlike two-stroke analogues, where oil is mixed with gasoline, in the 4t engine, the lubrication and gas distribution system creates additional resistance when scrolling with the starter.
In this article, we will discuss in detail why startup problems arise, which nodes to check first and how to set up a carburetor for a confident start. Systems approach The diagnostics will save you time and return the two-wheeled friend to the line without unnecessary costs.
Features of starting a cold 4t engine
The problem of cold start lies in the physical properties of gasoline and the state of the engine parts. When the engine cools, the walls of the cylinder and intake manifold become cold. When there is a fuel mixture, part of the gasoline condenses on the walls, not having time to evaporate. As a result, the combustion chamber is slurrywhich is not sufficient to ignite.
In addition, cold engine oil has a high viscosity, which creates significant resistance to moving parts. Starter, especially on budget models of scooters 50 cc, it can be difficult to turn the crankshaft at the right speed. If you add here the possible discharge of the battery, the picture of an unsuccessful start becomes quite understandable.
It is important to understand that the state of the gas distribution system is critical for the 4t engine. Valve gaps, which can be normal on hot, on a cold engine can significantly affect compression. The loose fit of the valves due to improper adjustment is a common reason why the scooter stalls immediately after the start or refuses to start at all.
Fuel system: carburetor and quality of mixture
The most common reason why the scooter is not started on a cold one is the wrong work of the carburetor. It is this unit that is responsible for the preparation of the combustible mixture. If the fuel level in the float chamber is too low or the jellyfish are contaminated, the engine will not receive the desired portion of gasoline. Especially important. idle-jackIt delivers fuel before the throttle is opened.
Many owners forget about the system of enrichment of the mixture during cold start. Depending on the model, it can be manual. enricher (suction) or automatic starter enricher (electrovalve). If the electric valve is faulty or does not come to the voltage, the mixture remains poor, and the motor refuses to work without warming up.
- 🔧 Pollution of jellystones by deposits of resins - requires complete disassembly and washing of the carburetor in an ultrasonic bath.
- 🔧 Faulty starter enricher - the needle does not block the channel after warming up or does not open it to the cold.
- 🔧 Suction of air through the sealing rings - leads to a strong impoverishment of the mixture and unstable operation.
- 🔧 Low fuel level in the tank or a clogged fuel filter is a banal, but common cause of starvation of the engine.
The quality of the fuel itself deserves special attention. Gasoline that has been in the tank for more than a month loses its octane properties and evaporates, leaving heavy fractions. This “old” gasoline burns worse, which is especially noticeable on a cold engine. It is recommended to drain fuel during long-term storage of equipment.
Before a long parking (winter), always close the fuel crane and generate the residue of gasoline from the carburetor to avoid coking the channels.
Ignition system: candles and coils
The second most important group of causes is spark formation. Even if the mixture is perfect, without a powerful spark of ignition will not occur. On a cold engine, the requirements for spark quality are higher, since the air density in the cylinder is greater and the compression temperature is lower. A faint spark simply sinks in the flow of cold air and fuel.
The first thing to check is spark-plate. Visual examination of the garment can tell a lot. Black soda indicates a rich mixture or poor combustion, white - about overheating or poor mixture. If the candle electrodes are melted or covered with oil plaque, the spark will skip unpredictably or go to the mass.
It is also worth checking the gap of the candle. For most 50 cubic 4t scooters, it should be 0.6–0.7 mm. Too much gap requires high voltage, which an old coil or CDI unit may not provide. Too small a gap gives a weak spark, which is not enough to light the mixture.
How to check the spark safely?
Unscrew the candle, press it with a thread to the clean metal part of the engine (cylinder) and spin the starter. The spark should be bright blue and audible. A red or yellow spark indicates problems with the coil or wiring. Do not hold the candle with your hands during the check.
Do not forget about the high-voltage cap. If it is oxidized inside or has cracks, some of the charge goes out, especially in wet weather. condensate On the ignition elements, enemy number one for cold launch.
Compression and condition of the cylinder-piston group
Compression is the pressure created in the cylinder during a compression stroke. For a confident start of 4 t engine 50 cubes, a pressure of at least 9-10 atmospheres is required. If the compression is lower, the mixture does not warm up to the temperature of self-ignition, and the engine does not start. The fall in compression is often associated with the natural wear of the piston group.
The main reason for loss of compression to cold is the gaps between the piston rings and the walls of the cylinder. When the metal is cold, the gaps are maximum and the gases break into the crankcase. As the piston warms up, the gaps decrease, and the compression increases. That is why the worn-out motor can start only after warming up or from the pusher.
| Status of the CPG | Compression (cold) | Probability of launch | Recommended action |
|---|---|---|---|
| New engine | 11-12 atm | Instant. | Regular service |
| Normal wear and tear | 9-10 atm | Good. | Control of oil levels |
| Critical wear and tear | 6-8 atm | Difficult/Impossible | Ring replacement or seedling |
| Cylinder bully | < 5 atm | Absent. | Major overhauls |
You can check the compression using a special compressometer, which is screwed in instead of a candle. If there is no tool at hand, you can use the "grandfather" method: plug the candle hole with your finger and spin the starter. The finger should be pushed out, and in the presence of compression it will be difficult to hold.
A compression drop below 8 atmospheres makes normal start-up of the 4t engine almost impossible without preheating or using esters.
Valve adjustment: the hidden cause of problems
In four-stroke scooters, 50 cubes are often forgotten about valve adjustment. Thermal gaps in the valve mechanism are not a whim, but a necessity. When heated, the metal expands, and if there is no gap, the valve will not sit tightly in the saddle, which will lead to burnout and loss of compression.
However, if the gaps too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too-too (which often happens when the wear of rockers and valves), then on a cold engine, the valve will open later and close earlier than set. This reduces the time of filling the cylinder with fuel and worsens purge. The engine is "choking" and not starting well. Optimal clearances are usually 0.05 mm for the intake valve and 0.10 mm for the exhaust valve (see the exact value in the manual for your valve). motor).
Adjustment is carried out on a cold engine. It is necessary to place the piston in the upper dead point (BMT) of the compression stroke (the mark on the crankshaft coincides with the risk, both valves are closed). Then the gap between the valve and the skewer is checked with a probe. Adjustment is made by a screw and a counternut.
- 🛠️ Too small gap: risk of valve burnout, loss of compression on hot.
- 🛠️ Too big a gap: knocking in the cylinder head, difficulty starting to cold.
- 🛠️ Frequency of check: every 3000-5000 km run.
Incorrect valve adjustment is one of those reasons that is easy to miss, changing candles and carburetors. Make sure that this procedure is done well if other methods do not help.
Effects of motor oil and ambient temperature
Motor oil plays a critical role in the launch. For 4t scooter engines, it is important to use oil with the correct viscosity. If you pour too thick oil (like 20W-50) before winter, the starter simply won’t be able to pull the crankshaft at the right speed. The engine will growl, but it will not start.
In winter or at temperatures below +5°C, it is recommended to switch to more liquid synthetic oils, for example, 5W-40 or 10W-40. They keep fluidity in the cold, providing normal scrolling and lubrication in the first seconds of operation. Also, the oil level should be normal: a low level leads to dry friction, high - to foaming and difficulty in rotating the crankshaft.
⚠️ Attention: Never use oils labeled "JASO MA/MA2" for dry clutch scooters unless the manufacturer indicates otherwise, although this is less critical for 4t engines than for 2t. The main thing is the correspondence of viscosity to air temperature.
In addition, cold air is denser than warm. A carburetor tuned for the summer heat will produce a too poor mixture in winter. Some carburetors have the option of adjusting the position of the needle or replacing the chicklers with a winter kit, which solves the problem of cold start.
☑️ Diagnosis of cold start
Frequent Questions and Answers (FAQ)
Why is the scooter started only with a closed air valve?
This is a classic sign of a depleted mixture. A cold engine needs more fuel. If you have to keep the valve (suction) closed constantly, it means that either the main jikler is clogged, or the air sucker in the intake tract, or the fuel level in the float chamber is incorrectly configured.
Can I spray a quick start into a carburetor?
Ether-containing sprays can be used, but with extreme caution. Frequent use of "Quick Start" washes the oil film from the piston, which leads to accelerated wear. It is a tool for emergency cases when you need to check for spark and compression, and not for daily use.
The scooter starts and immediately dies, what is the matter?
Most often the problem is in the idling system or the starter enricher. The engine is started on an enriched mixture, but once the speed drops to idle, the fuel supply stops or too little air enters. It is also worth checking the idle valve if it is on your model.
How often should I change the candles on a 50cc scooter?
The resource of a conventional nickel candle is about 3000-50,000 km. Iridium lasts longer, up to 10,000 km. However, if there are signs of poor start, trim or increased fuel consumption, the replacement should be made earlier, without waiting for the planned maintenance.
Does a clogged air filter affect the launch?
Yeah, a lot. If the filter is clogged with dirt, little air enters the carburetor, the mixture becomes overenriched. The engine is "choked" and cannot start. On the other hand, if the filter is removed completely, the mixture will be poor. The filter must be clean and installed in place.