1) Start at the top. Check the plug cap and replace the spark plug first of all.
2) Disconnect any kill switch if fitted.
3) Unscrew the plug cap, and check to see if the spark will jump 5mm from the end of the wire to earth when cranking the engine over by hand. If it does, check the condition of the plug cap, replace and try again. If the spark will not jump the gap, you have a problem. Read on....
4) Check the H.T. lead and L.T. connections at the coil for frayed wires & poor connections.
5) Check to see if the points gap is correct (.018"), also check to see if the points are chipped, contaminated with dirt/oil/corrosion or if the contact faces have come loose. Replace if suspect. Part No. 869517.
6) Check to see if the copper strip joining the rocker arm to the base plate, is shorting out to earth also check if the contact breaker cover is not touching the contacts or copper strip when in place.
7) Check to see that the condenser has a good earth.
8) If the points are sparking excessively, the condenser may be faulty. Replace if suspect. Part No. 31297FB.
9) Check to see that the cam has been installed correctly (look for the direction arrow).
10) Check up and down movement on the crankshaft excessive play in the main bearings can cause misfires at mid to top end running.
11) Check to see that the flywheel is tight on it's taper.
12) Remove the flywheel and check to see if the L.T. lead to the points, has chafed through on the back of the flywheel.
13) Check the condition of the connections on the stator. Some original stators suffer from coils working loose and poor joints, especially where the rivet passes through the L.T. tag.
14) Check the earth lead for bad joints and poor grounding.
15) Check the coil connections. The wire from the points goes to + (terminal 15)

Note: If the engine has been running for some time with the coil wired the wrong way round, the coil may be producing a weakened spark which will fail under compression. The spark will look nice and blue, but the engine will not start. This can be very misleading because the plug will appear to have a nice blue spark when you check it, the plug will be getting wet but the bike will not start.