How to diagnose Visual inspection
First, Check for loose the coil to distributor high tension cable and low-voltage circuit between ignition coil and distributor. If so, restart the engine and see if it can be started after troubleshooting. If the\tvisual examination does not find any problem, proceed to the next troubleshooting step.
Pull out the coil to distributor high tension wire, and make the spark plug wire terminal 5-8mm away from the engine block, then turn on the ignition switch, when start the engine with the starter, see whether to spark jump between the spark plug wire terminal and the engine block. There are three cases：The spark is strong; the spark is weak or the spark jumps.
A. If the spark is very strong, it indicates that the low-voltage circuit and ignition coil is basically normal. While the fault is in the high-voltage circuit or spark plug, proceed to carry out the next step fault diagnosis.
B. If the spark is very weak, it may be caused by faulty components, such as breaker, capacitor and ignition coils, or poor connection of spark plug wire. Further diagnosis can be made in step (4).
C. If there is no spark, the possible causes of the fault include poor contact of the breaker, the movable contact point ground or short circuit of capacitor, short circuit or open circuit of the ignition coil, or poor contact of the ignition switch and ignition coil low-voltage circuit. Step 5 can be used for further troubleshooting.
Spark plug wire test
Insert back into the Spark plug wire, pull out the spark plug wire on a cylinder spark plug for test, and make the spark plug wire terminal 5-8mm away from the engine block. If the spark does not jump or the spark is very weak, it indicates electric leakage or open circuit in distributor cap, rotor or spark plug wire, these parts need to be repaired. If the spark is still strong, the spark plug shall be removed for inspection. If the spark plugs of all cylinders are in good condition, then check the oil circuit, ignition timing and other possible faults that may cause the engine to fail to start.
Diagnose the cause of weak spark with instantaneous short circuit method
When the breaker contact is open, turn on the ignition switch, and conduct jump spark test of the high tension lead by instantaneous ground between the "-" terminal of ignition coil (leaving quickly after wire the terminal is grounded), to see whether the spark at the terminal of the spark plug wire becomes stronger. If the spark becomes stronger, it is necessary to check the contact of the breaker, capacitor and other components; If the spark is still weak, check or replace the ignition coil.
Diagnose the cause of no spark jump with instantaneous short circuit method
When the breaker is disconnected, the ignition coil "-" and conduct jump spark test of the high tension lead by instantaneous ground between the ignition coil. If there is jump spark, it is necessary to check breaker contact, capacitor and other components. If the spark is still not jumping, then see if there is a spark when grounding at the moment. If not, check whether the low-voltage loop circuit of the ignition system is open circuit or the primary winding of the ignition coil is open circuit; If there is a spark when contacting. check whether the secondary winding of the ignition coil is open or short circuit fault, and whether high tension lead is open circuit.
James Smith 
July 14, 2020