The thermal scooter is equipped with a two or four-stroke engine. This engine may itself be injection indirect by carburetor or direct injection by injector. The misfire corresponds to a malfunction of the scooter due to incorrect operating parameters. It is materialized by an irregular engine noise which characterizes it but also by jerks in acceleration. Misfiring leads to overconsumption of fuel and can cause the engine to stall.
Scooters - general information
Here is an article that serves as a guide and helps you choose your scooter better before purchasing. For this, we give you the details on the characteristics and the different types of scooter.
Operating principle of an engine
The principle of operation of the engine, whatever the type of engine, is practically the same: air is sucked in by vacuum when the piston goes down to bottom dead center and is injected into the engine. This volume of air is mixed with gasoline before they are injected into the engine (carburetor type) or mixed with gasoline directly in the engine by injectors. The resulting explosion is achieved by an ignition system that activates one spark plug per cylinder.
This spark plug is activated when the gasoline-air mixture is compressed to its highest level when the piston is at top dead center, the highest position of the cylinder in a combustion chamber. The synchronization of the spark plug ignition period with respect to the high position of the piston and the closing of the valves if a four-stroke engine determines the ignition timing (not to be confused with the engine timing which is the 'sudden engine shutdown due to breakdown).
Scooter that has misfires due to an inadequate air / fuel mixture
The misfire from the air / fuel mixture is due to a poor mixing ratio. The optimum rate to keep the engine running smoothly or to avoid a misfire is about 15 grams of air for one gram of gasoline. When there is less air, the mixture is enriched in gasoline and creates misfires. When there is more air for less gasoline, the mixture becomes depleted in gasoline and can cause misfires or even failure, as there is a risk of the engine overheating. Whether for a scooter or for a motorcycle the resolution of the problem is quite similar.
There are two ways to know if the air / fuel mixture is correct:
- The first way is to measure this mixture using a measuring device available on the market.
- The second way is to rely on the color of the spark plug electrode. If the color is black, the mixture is too rich. If the color is white, the mixture is too lean. If the color is brown, the ratio of the air / fuel mixture is good.
Scooter that misfires: Check the carburetor or injector
In the case of an indirect injection engine, the mixing took place outside the engine within a carburetor. To act on the carburetor to obtain a good mixture, it suffices to intervene on the mixture screw by screwing it completely then by unscrewing it by quarter turn of the screwdriver to obtain the good idle speed and, consequently, the good mixture.
In the case of a direct injection engine where mixing has taken place in the engine cylinder at the intake time, it will be necessary to check the efficiency of the flowmeter which is a device supposed to regulate the volume of air. The flowmeter is placed in the air intake circuit after the air filter. It is fitted with a valve which is sensitive to the speed of the air (its flow rate) and which returns information on the density of the air to the computer, the engine computer. The latter will thus gauge the quantity of air necessary to mix with the gasoline in the engine. Thus, a faulty flowmeter will return false information to the ECU and therefore send the wrong amount of air volume to the engine.
Scooter that misfires due to improper ignition timing
The correct ignition timing thus results from three parameters: the accuracy of the quantities mixed of air with gasoline once compressed, the highest position of the piston and the quality of the spark supplied by the spark plug. If one of these two parameters is faulty then the scooter risks having misfires. To produce a failure-free explosion, the engine piston must be at its highest level, at top dead center or TDC. In this position, the valves (if a four-stroke engine) must be closed. Also at this position, the spark plug must provide a spark intended to detonate the compressed air / gasoline mixture. The valves (if a four-stroke engine) must be closed. If any of these parameters are not respected, the system will produce misfires.
Scooter that has misfires due to poor ignition quality
The performance of the spark plug determines the proper functioning of the engine without misfire but also the power of this engine. A spark plug that is not supplied with high voltage electric current by the coil or by the rotor causes misfires. Sometimes a spark plug that sparks out of timing of the ignition timing will also misfire. In this case, it will be necessary to check the entire electric circuit of the scooter.
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