well there isnt much to a points ignition circuit really .firstly you have the primary ignition coils and then the live wires from that goes to the top of the condensers these then link to the points and then up t the secondary ignition coils.so you need to firstly check your primary coil is ok try wiring the wire from the working cylinderi.e 1+4 to the non working one 2+3 so basically take the wire off the primary coil running the working ones and put it to the points and condenser of the non working ones.see if it sparks then on that cylinder.if it doesnt then its not the primary coil.if it does then it is.so if it still doesnt it means its either the points dirty or maladjusted or the condenser is either faulty or shorting to earth the points also need to be insulated where the live wire goes there should be a bakerlite washer there.if neither of these seem to be the problem then it may be the wire from the non running cyclinders points that is shorting to earth on its way up to the secondary ignition coil.the scondary coil has 2 terminals usually one pulsing live from the points and a constant earth if it only has one wire then the coil itself must have a good earth were its bolted to the frame and also the engine must be earthed to the frame seeing as one cylinder is sparking it should not be hard to suss out what is the problem as you can swap bits about to see if anything makes it work.
adam bike doctor(of milton keynes motorcycle centre), October 2010
