Malfunction | Manifestation and possible causes | Remedy |
The engine does not start or is difficult to start. | Low compression | |
1. Valve clearance is not adjusted. | Adjust. | |
2. Worn valve guides or incorrect valve seat clearance. | Repair or replace. | |
3. Valve desynchronization. | Tune. | |
4. Wear of piston rings. | Replace. | |
5. Development of the cylinder. | Replace. | |
6. Slow starter rotation. | See the electrical equipment section. | |
7. The spark plug is loose. | Tighten. | |
No spark at the spark plug | ||
1. The spark plug is dirty. | Clean or replace. | |
2. Wet spark plug. | Clean and dry. | |
3. The generator or CDI unit is faulty. | Replace. | |
4. The ignition winding is faulty. | Replace. | |
5. Break or short circuit of the high-voltage wire. | Replace. | |
Fuel does not enter the carburetor | ||
1. The fuel tank cap is clogged. | Clean or replace. | |
2. The fuel valve is clogged or faulty. | Clean or replace. | |
3. The needle valve is faulty. | Replace. | |
4. Fuel or vacuum hose is clogged. | Clean or replace. | |
5. Fuel filter is clogged. | Clean or replace. | |
The engine stalls | 1. The spark plug is dirty. | Clear. |
2. The CDI unit is faulty. | Replace. | |
3. Fuel hose is clogged. | Clear. | |
4. The jets in the carburetor are clogged. | Clear. | |
5. Valve clearance is not adjusted. | Adjust. | |
Extraneous noise in the engine | Loud knocking of valves | |
1. Large valve clearance. | Adjust. | |
2. Weak or broken valve springs. | Replace. | |
3. Camshaft wear. | Replace. | |
4. Wear or burnout of the camshaft journal. | Replace. | |
Loud noise from piston | ||
1. Worn piston or cylinder. | Replace. | |
2. Carbon deposits in the combustion chamber. | Clear. | |
3. Wear of piston pins. | Replace. | |
4. Development of piston rings or their grooves. | Replace. | |
Loud noise from timing chain | ||
1. The timing chain is stretched. | Replace. | |
2. Sprocket wear. | Replace. | |
3. The chain tensioner does not work. | Repair or replace. | |
Loud noise from clutch | ||
1. Worn transmission shaft splines or clutch disc hub. | Replace. | |
2. Wear of teeth on clutch discs. | Replace. | |
3. Deformation of clutch discs, driven and driven. | Replace. | |
4. Worn release bearing. | Replace. | |
5. The clutch spring is weakened. | Replace. | |
6. The clutch damper is weakened. | Replace the drive gear. | |
Loud noise from crankshaft | ||
1. Bearing noise. | Replace. | |
2. Wear or burnout of bearings. | Replace. | |
3. Bearing wear or burnout is large (bottom) connecting rod heads. | Replace. | |
4. Large axial clearance of the connecting rod. | Replace. | |
Loud noise from transmission | ||
1. Gear wear. | Replace. | |
2. Worn transmission shaft or drive shaft splines. | Replace. | |
3. Wear of drive gears. | Replace. | |
4. Excessive wear of bearings. | Replace. | |
Clutch slipping. | 1. Incorrect clutch cable tension. | Adjust. |
2. The clutch springs are weakened. | Replace. | |
3. Wear or deformation of the pressure plate. | Replace. | |
4. Clutch discs, driving and driven, are deformed. | Replace. | |
The clutch does not disengage completely. | 1. Incorrect clutch cable tension. | Adjust. |
2. Several clutch springs have weakened, but the rest have not. | Replace. | |
3. Deformation of the pressure plate and clutch discs. | Replace. | |
Unable to switch gears. | 1. The cam of the gear shift mechanism is broken. | Replace. |
2. The forks of the gear shift mechanism are deformed. | Replace. | |
3. The gear shift pawl is worn. | Replace. | |
It is impossible to turn off the transmission. | 1. The return spring of the gear shift shaft is broken. | Replace. |
2. Wear or «sticking» gear shift shaft. | Replace. | |
3. The gearshift forks are deformed or worn. | Replace. | |
The engine does not idle smoothly. | 1. Valve clearance is not adjusted. | Adjust. |
2. Incorrect valve seat clearance. | Replace or repair. | |
3. Valve guides are faulty. | Replace. | |
4. The camshaft is worn out. | Replace. | |
5. The ignition winding is faulty. | Replace. | |
6. The generator or CDI unit is faulty. | Replace. | |
7. Insufficient spark plug gap. | Replace or adjust. | |
8. Incorrect fuel level in the carburetor float chamber. | Adjust the height of the float. | |
9. Carburetor jets are clogged. | Clear. | |
The engine does not operate stably at high speeds. | 1. The valve springs are weakened. | Replace. |
2. Valve desynchronization. | Adjust. | |
3. Worn cams or camshaft. | Replace. | |
4. Insufficient spark plug gap. | Replace or adjust. | |
5. The ignition winding is faulty. | Replace. | |
6. The generator or CDI unit is faulty. | Replace. | |
7. Ignition is not effective due to poor performance of the timing circuit. | Replace the CDI unit. | |
8. Low fuel level in the carburetor float chamber. | Adjust. | |
9. The air filter is dirty. | Clean or replace. | |
10. The fuel hose is dirty, which prevents fuel from entering the carburetor. | Peel and shed. | |
Smoky or dirty exhaust | 1. Excessive amount of engine oil. | Drain off excess oil. |
2. Worn piston rings or cylinder. | Replace. | |
3. Worn valve guides. | Replace. | |
4. Scratches or abrasions on the cylinder wall. | Replace. | |
5. Worn valve stems. | Replace. | |
6. Rod seals are faulty. | Replace. | |
7. Worn oil scraper rings. | Replace. | |
Insufficient engine power. | 1. There is no valve clearance. | Adjust. |
2. The valve springs are weakened. | Replace. | |
3. Valve desynchronization. | Adjust. | |
4. Worn piston rings or cylinder. | Replace. | |
5. Incorrect valve seat clearance. | Replace or adjust. | |
6. Spark plug dirty. | Clean or replace. | |
7. Incorrect spark plug gap. | Replace. | |
8. Carburetor jets are clogged. | Adjust or replace. | |
9. Incorrect fuel level in the carburetor float chamber. | Adjust the height of the float. | |
10. The air filter is clogged. | Clear. | |
11. Excessive amount of engine oil. | Drain off excess oil. | |
12. Air leak from the inlet pipe. | Adjust the height of the float. | |
13. The generator, ignition winding or CDI unit is faulty. | Replace. | |
The engine gets very hot | 1. Significant carbon deposits on the piston head. | Clear. |
2. Insufficient amount of engine oil. | Check oil level. | |
3. The oil pump is faulty or the oil circuit is clogged. | Replace or clean. | |
4. Low fuel level in the carburetor float chamber. | Adjust the height of the float. Tighten or replace. | |
5. Air leak from the inlet pipe. | Replace. | |
6. Poor condition of engine oil. | Clear. | |
7. Oil cooler is clogged. |