I've been driving and maintaining "Furgie", Daimler V250, for over 25 years. But am temporarily stumped with this one:
Installed a rebuilt distributor with new points, etc. and she performed beautifully. 100 miles into a road trip (with the wife aboard, of course) there was a sudden engine miss, then smoke from under the hood. That turned out to be a short in the wiring harness crossing from the left headlight section to the right. I temporarily insulated the burned wires and went on my way. 30 minutes later she started missing, then would clear and run fine, then miss. Next morning would not start, no spark. Then started and ran fine, then missed, stalled etc. This pattern continues to today, but is getting increasing worse. To be brief, here is what I did over a period of 5 days:
Replaced dizzy cap, rotor, contact points, condensor. Bypassed the doubtful looking insulated distributor terminal (wired the coil directly to condensor.) Temporarily hot wired (bypassed the ignition switch.) Temporarily bypassed the + coil wire running through the harness by running a direct wire to the distributor. Rechecked timing, carburetion, battery ground
I have checked and rechecked every aspect of the ignition loop that I can think of but she still poops with poor spark.
I just got her towed back home yesterday so I can troubleshoot at leisure now.
Here is what I have not done yet:
New HT wires (not in stock at sng Barrett)
Checked the engine ground. ( assume this is at the starter)
- I cannot imagine that short creating the problem, but I keep going back to it. Is there a chance that an intermittent short inside the harness can cause the ignition issues?
I'd appreciate any thoughts, I start on her tomorrow.

 

I would certainly replace any burnt, chafed or suspect wiring.

If you have an intermittent ground fault on the ignition circuitry then as it grounds it will reduce the voltage and hence current flow to the coil, thereby reducing the spark considerably if not altogether, leading to your misfire symptoms.

Engine ground will be on the starter but there may be others so have a good look around but sort the wiring first.

 

Ignition circuitry is good. I replaced or bypassed all of it. The short in the headlight wiring has a temp fix using butt connectors. All lights work properly.

 

Do you have a fire extinguisher handy _ a large one ? Electrical fires can get out of hand very quickly, people think they have enough time to run in the house and grab one, but it's usually too late.
I know of a guy who had a short in the wiring with his early 50's Rolls _ no fire extinguisher handy. By the time he grabbed one, it was too late, he lost the Rolls and the mew Mercedes parked behind it. The fire got so hot it melted the aluminum body on the Rolls.
When I belonged to the Rolls Bentley club you were not allowed to take part in club events unless you had one in the boot.

 

It's always easily accessible in trunk. Just a note to anyone else with the V8, when ethanol eats the jet diaphragm in your SU carbs, fuel pours directly onto the manifold.

 

Somehow the coil + and - wires got switched. Probably burned up a coil or two. Anyone know how to bench check? Anyway, the car has good fire. She idles rough which should be expected on a cold engine. When I give her any choke or throttle she stalls.

 

I just got back on the forum and posted a fog light hack to replace the old incandescent s with LED's and see that I never posted the solution to my old hair pulling ignition issue. Here goes: Eventually the thing degenerated to the point where it would start and idle but as soon as you touch the throttle it would die every time. I pulled the distributor and in process of dismantling noticed that one of the point support posts was loose. It wiggled just slightly when touched. Braised it and have been running strong ever since.

 

Thanks for following up. Always interesting to hear how strange problems are solved.