old engine ran fine for months on old roller timer and home rebuilt coils until 4 new coils and a new tw timer ,took timer off and found that the pick up points on the timer were burnt on the end of timer not at the start and have had nothing but troubles since, back firing loss of power but go back to old roller timer every thing ok being in mind motor 85 year old untouched, then get a completely new block new rebuild ,new mag plate the whole works new coil box new anderson type timer checked chassis to engine block earth the whole lot
new start every thing ok but slowly deteriorating in timing and today take flapper timer off and to find a wearing burning at the back end of pickups and rotor ?
so question is what could be causing a burning and an engine surging trying to run?
sounds like weak voltage.. and the burning caused by short arc due to high amps. Remember when voltage goes up amperage goes down, and when voltage goes down amperage goes up. You say you checked the earth (ground). Is there any corrosion in the positive wires at all???
Not saying I am right.. there is a lot smarter than me here.. but that is where I would look first.
And again... That's just me.