18rg ignition spark dodgy

[DaveSpec]

I've finished building my 18rg and have put it in my ra40 and am up to running the new girl. So i turn the key, engine starts perfectly, and check the ignitoin timing with a timing light. I've found so far that cylinders 1 and 2 will fire evey time without fail but 3 and mostly 4 can miss a spark every now and then. I have tried many different leads and when i put them on cylinder 4 they become dodgy even when they were working fine before.
The distributor is straight out of another working engine so pretty sure thats fine.
Have used 2 different coils and they both produce the same result.
I'm thinking maybe there is something wrong with my wiring. Would like to just rewire it all but i don't have a complete wiring diagram for the resistor and coil.

Any ideas what might be causing this?

Any help would be greatly appreciated

[Rodger]

Can I assume new plugs?

Try swapping plugs around keeping the leads on the same cylinders. Old or new plugs then this would show if the problem moves with the plugs.

If the engine is really rich at idle then the plug maybe too wet to spark and cause the timing light to flash. If the dizzy is mechanical points, is there actually a gap? If not enough gap then the lobes on 3 and 4 could be worn a fraction compared to the other two.

There is only one wire from the dizzy and it comes from the coil. A faulty wire here would cause a random misfire or no spark at all. Same with the positive wire to the ballast resistor and then the coil, if it were loose or faulty.

Regards
Rodger

[DaveSpec]

Yeah plugs are new.
Seem to have it working now i took the 3 and 4 plugs out, cleaned them (completely black and wet) and swapped them and they seem to both fire properly now. Did also wire up the coil so i dont use the ignition switch for it because i dont trust it yet. Guy before me relocated the coil and use thinner wires and ducttape so didnt trust that....
Thanks for the help