My two cents (and apologies if I'm giving egg sucking lessons):
You don't say whether you've checked the distributor rotor for HT leakage to earth (as suggested by John C)?
The usual side of the road method is to remove the centre HT lead (the one which goes to the coil; what some call the "king" lead) from the distributor cap, and with the cap removed, so you can see them, rotate the engine until the contact breaker is closed, switch the ignition on and holding this lead 1/4 inch from the rotor, snap the CB points open, either with your thumb (or a screwdriver if like me, you're not shock resistant...) Any sign of a spark to the rotor is a fail. Pro tip, insulated pliers are your friend for holding the lead.
Extra edit: Also try directly filling the float bowl of the carburettor with fresh fuel with the pump to carburettor pipe disconnected (you will have to arrange some method of avoiding fuel flow from the plumbing if you do this for safety). This will eliminate all fuel components except for the carburettor.
There are lots of real experts on here who have real world experience that will chime in I'm sure.
You don't say whether you've checked the distributor rotor for HT leakage to earth (as suggested by John C)?
The usual side of the road method is to remove the centre HT lead (the one which goes to the coil; what some call the "king" lead) from the distributor cap, and with the cap removed, so you can see them, rotate the engine until the contact breaker is closed, switch the ignition on and holding this lead 1/4 inch from the rotor, snap the CB points open, either with your thumb (or a screwdriver if like me, you're not shock resistant...) Any sign of a spark to the rotor is a fail. Pro tip, insulated pliers are your friend for holding the lead.
Extra edit: Also try directly filling the float bowl of the carburettor with fresh fuel with the pump to carburettor pipe disconnected (you will have to arrange some method of avoiding fuel flow from the plumbing if you do this for safety). This will eliminate all fuel components except for the carburettor.
There are lots of real experts on here who have real world experience that will chime in I'm sure.