1. The engine cannot be started or is difficult to start
(1) Fault symptoms
① The starter cord pulls normally, but the engine cannot be started and there is no response.
② The exhaust pipe emits black smoke, but the engine cannot start even when it is ignited.
③ The carburetor keeps leaking oil outward.
④ It cannot start, there are sparks at the spark plug, the electrode is damp, and there is a strong smell of gasoline.
⑤ When using a manual starter or electric starter, the engine feels very easy to turn, and even when compression ends, it still feels very little resistance.
⑥ The engine has no compression, and it is not easy to ignite and start, but the exhaust pipe has backfire.
⑦ When starting the engine, there is backfiring; when using the carburetor, there is backfire.
(2) Causes of the fault
① The ignition switch is short-circuited to ground (electric-start models).
② The spark plug is damaged; the spark plug electrode gap does not meet the standard, and the spark plug is dirty and wet, resulting in poor insulation.
③ The high-voltage wire is detached, or the insulation is poor, causing leakage; the igniter is faulty or punctured.
④ There is no fuel in the fuel tank; the fuel switch is not opened; the fuel tank cap vent hole is blocked.
⑤ The fuel filter screen is blocked; fuel flow in the fuel line is obstructed; the needle valve is stuck and cannot move; there is water in the carburetor float chamber; the carburetor passages (including the main nozzle, main metering hole, idle metering hole, etc.) may be blocked; the needle valve is not closed tightly; the float is leaking, or the fuel level is adjusted too high; the main metering hole is severely worn, increasing the fuel injection cross-section.
⑥ The spark plug is not tightened; the spark plug gasket is damaged; the valve clearance is too small, and the valve leaks because of carbon buildup.
⑦ The ignition timing is too early or too late.
⑧ The cylinder gasket is damaged.
⑨ Severe wear between the cylinder and piston rings; the piston rings (gas rings and oil rings) lose elasticity, or the piston rings are damaged; the piston rings are severely worn or damaged.
(3) Troubleshooting methods
① For electric-start models, if the engine can be started by hand pulling, it indicates a short circuit of the ignition switch to ground or a fault.
② Check the spark plug for skipping ignition. Remove the spark plug, insert it into the spark plug cap, let the metal shell of the spark plug contact the engine metal parts, repeatedly pull the starter cord, and observe the spark plug electrode for ignition skipping. A blue-white spark means normal ignition; no spark or a red spark indicates a fault. If the spark plug does not spark, check whether the igniter and high-voltage wire are damaged. Remove the high-voltage cap, take a short piece of metal wire and insert it into the high-voltage wire, keep a gap of about 0.7mm between the metal wire and the metal parts of the engine, and if there is no spark, it indicates a faulty igniter.
③ Check whether the spark plug ceramic body is cracked, whether the center electrode is corroded or damaged, and if so, replace the spark plug; if the spark plug is too dirty, it can be cleaned with gasoline, then the electrode gap should be adjusted to the specified value before drying and using again. Check whether the connection between the high-voltage wire and the spark plug connector is secure; replace the connector if necessary.
④ Check whether there is gasoline in the fuel tank, then carefully check whether the fuel switch is open, and then unclog the fuel tank vent hole so that the tank and the atmosphere are connected to form a pressure difference.
⑤ Remove the pipe connecting the carburetor to the fuel tank; fuel should flow out. If no fuel flows out, remove the fuel filter and clean it; if fuel flows from the hose, check the fuel inlet condition of the carburetor, and use a screwdriver to loosen the carburetor drain screw. If the fuel level is too low, the needle valve may be stuck; remove the carburetor to see whether it can move. Check whether there is water or dirt in the float chamber, whether the main nozzle, main nozzle port, main metering hole, idle metering hole, etc. are blocked, or thoroughly clean the carburetor; if the carburetor fuel level is too high, it may be that the needle valve is not closed tightly, the float is leaking, or the fuel level is adjusted too high, or the main metering hole is severely worn, resulting in an increased fuel injection cross-section.
⑥ First check whether there is a gasket on the spark plug, or whether the gasket is contaminated with dirt, and then tighten the spark plug to the specified torque. For a four-stroke engine, if the valve clearance is too small, remove the cylinder head or the screws on the side cover plate, then turn the engine to the compression stroke top dead center and use a thick-thin gauge to adjust the valve clearance.
⑦ For an overhead-valve engine, if there is no compression when starting and it is difficult to ignite, but there is backfire in the exhaust pipe, it indicates that the ignition timing is too late; if there is backfiring when starting the engine, or backfire in the carburetor, it indicates that the ignition timing is too early; check the causes of the ignition timing deviation of the engine.
⑧ If there is leakage between the cylinder body and cylinder head, check whether the cylinder head studs are tightened or whether the tightening force is symmetrical. If leakage continues, check and replace the cylinder head gasket.
⑨ Check the cylinder compression pressure, which can be checked by experience. Slowly pull the starter cord; if there is a resistance feeling, compression is normal; if there is no resistance feeling, it indicates no compression. If there is no compression, check whether the valve clearance is normal.
2. Engine power shortage or accelerated flameout
(1) Fault symptoms
① The engine is relatively difficult to start.
② Power performance has obviously declined. When the load is above 80%, the speed obviously drops or the engine stalls.
③ The speed cannot reach the rated value, and adjustment is ineffective. The carburetor is prone to backfire.
④ The exhaust pipe emits black smoke and makes a “puff-puff” sound or a pop sound.
⑤ The sound is uneven. During idle speed, the engine has severe periodic shaking.
(2) Causes of the fault
① Gasoline of the specified grade was not used, or gasoline that has deteriorated after long-term storage was used.
② The engine lubrication is poor.
③ The mixture is too rich or too lean.
④ The spark plug is short of ignition or has weak ignition.
⑤ The ignition timing is too early or too late.
⑥ The engine is overheated, the exhaust resistance increases, the exhaust pipe and muffler are deformed and blocked, or excessive carbon deposits cause blockage.
⑦ Engine leakage and the compression force of the cylinder decrease, causing intermittent operation.
(3) Troubleshooting methods
① Check the quality of the gasoline; check the quality of the engine lubricating oil.
② Check whether the air filter element is too dirty or blocked; clean or replace if too dirty.
③ If the mixture is too rich, check whether the choke is open and whether the air filter is too dirty. For carburetors with a main oil needle, the main oil needle can be adjusted. If oil seepage appears in the carburetor, it means the oil level is too high; the oil level can be lowered or it can be checked whether the inlet needle valve is not closed tightly. If the mixture is too lean, check whether the main metering hole is blocked, whether there is water in the float chamber, whether the fuel level in the float chamber is too low, whether the filter screen at each fuel inlet is too dirty, whether the needle valve and fuel line are blocked. The fuel level and fuel needle can also be adjusted to increase the fuel injection amount.
④ When there is a spark plug short-ignition fault, remove the spark plug and test spark. The spark will appear intermittent and irregular. When the spark plug short-ignites or the spark is too weak, the engine will not burn completely, the speed will rise and fall suddenly, and this fault should be eliminated according to the content related to short ignition or weak ignition faults.
⑤ When the ignition timing is too early, there will be backfiring during startup, and carburetor backfire, early combustion, and explosion vibration may occur; when the ignition timing is too late, there will be exhaust pipe popping, engine overheating, etc. At this time, inspection and adjustment should be carried out according to the fault-related content of the ignition timing discrepancy.
⑥ Check whether there is carbon buildup or bending deformation inside the exhaust pipe and muffler.
⑦ Check whether the engine leaks air.
3. Engine unstable operation
(1) Fault symptoms
① The speed rises and falls suddenly.
② Carburetor backfire, exhaust pipe popping, and other phenomena occur.
③ It is prone to automatic flameout.
(2) Causes of the fault
① Mechanical failure of the speed regulating mechanism.
② Weak or intermittent high-voltage spark.
③ Ignition timing is too early or too late.
④ Excessive carbon buildup between spark plug electrodes.
⑤ The mixture is too lean.
(3) Troubleshooting methods
① Change the hanging hole position of the governor spring, or adjust the tail angle of the governor lever.
② Check the high-voltage input of the spark plug to determine the weak spark or intermittent spark location. High-voltage line leakage, bad igniter performance, generally replace it.
③ The carburetor of the extension engine is dirty or damaged, oil dirt has serious carbon buildup, the spark plug gap is too small, clean and adjust.
④ If ignition is too early or too late, there will be backfire or pop phenomena, replace it.
⑤ When the mixture is too lean, there is regular instability (stutter phenomenon), the oil level can be adjusted or the main fuel needle can be adjusted, and the air intake system should be checked for air leakage.
4. Automatic engine shutdown
The reasons for automatic shutdown are relatively complicated. Generally, the operation of the engine before automatic shutdown should be analyzed.
(1) Fault symptoms
① Normal automatic shutdown. There is no abnormal sound, and the speed drops from high to low until it stops smoothly through the transition.
② Abnormal automatic shutdown. There is abnormal sound before shutdown, the stop is sudden, and it is difficult to restart.
(2) Causes of the fault
① The fuel in the fuel tank is used up.
② The vent hole in the fuel tank cap is blocked.
③ There is water, dust, etc. mixed in the gasoline.
④ Air resistance. For example, when the engine is at four-high temperature, gasoline in the oil circuit evaporates.
⑤ The ventilating pipe of the crankcase is blocked.
⑥ The exhaust pipe is blocked and the waste gas cannot be discharged.
⑦ The combustible mixture is too lean; the ignition timing is too late.
⑧ The spark plug seal is not good and leaks air.
⑨ Poor valve grinding contact with the valve seat; poor sealing performance.
⑩ The cylinder head gasket is too thin or the combustion chamber has carbon deposits, resulting in too high a compression ratio.
(3) Troubleshooting methods
① Check the amount and quality of engine oil, and deal with any problems in time.
② Check the quality of the gasoline in the fuel supply system.
③ Check whether the load is too heavy and make adjustments.
④ Check whether the installation of the air-cooled system is correct, whether the airflow can flow normally, whether the heat sink is too dirty, and try to reduce heat resistance.
⑤ Check whether the vent hole of the crankcase is blocked.
⑥ The carbon deposits in the exhaust pipe and muffler should be cleaned thoroughly.
⑦ Check one by one the fault points that cause the extension engine mixture to be too lean and the ignition timing to be too late.
⑧ If the spark plug gasket is damaged, please replace it with a new spark plug. If the spark plug is found to be overheated, check whether its heat value meets the requirements; otherwise replace it.
⑨ If the valve leaks due to poor valve sealing, use grinding sand to grind the valve until the contact surface between the valve and the valve seat is complete and uniform. During inspection, it should not leak, and the valve clearance should be adjusted properly at the same time.
⑩ When the combustion chamber of the engine has carbon deposits, the cylinder head should be removed, the carbon deposits in the combustion chamber should be cleaned, and the cylinder gasket of the standard model number of the machine should be replaced.