Thank you for the continuing thoughts on our Dart problem... I had a good session on the car last night and, on the basis that a picture tells a thousand words, have captured a video of the symptoms!
But first, here's what I started with....
I started by checking the +ve and -ve wires were the right way round on the coil (they are) and verified that the spark wasn't leaking to earth via the rotor arm using the test outlined earlier (it wasn't). I also fitted my natty little spark tester device between one of the plug leads and insulating caps to check for spark. It has a massive fat spark on cranking. I checked the cap and rotor arm for any signs of tracking - none noted. There's no fuel leaks, no weeping float bowls, nothing obviously or even subtly erroneous that I can see....
With all checks done and everything confirmed as looking ok, I went for an evening test drive in the nice cool air...... As normal, it fired instantly on cranking and ran perfectly. Choke was used from cold and it benefits from that in fact. It runs SOoooo nicely when it's cold it's an absolute dream - it sounds fantastic, pulls like a train and is a massive pleasure to drive. I enjoyed a magical 5 miles of country roads at all throttle openings with it revving cleanly, pulling well and sounding ace! I'd dropped off the choke after a couple of miles as no longer required.
Then it began to miss the odd beat....
I elected to turn around and run for home again at that point, lest I experienced a 'failure to proceed' but popped the bonnet to check the spark on my tester first. The tester showed a decent spark still. I noted the Kenlowe had engaged to help cool the radiator, so engine temperature was spot on. As I retraced my steps it began to run rougher and rougher, feeling like it was dropping cylinders, not pulling, 'bellowing' if you could get it to the higher revs (I use the term bellowing as I don't know how else to describe it - it basically makes more noise but doesn't actually 'do' anything, no accelerative reaction). It's really not fun to drive when it's like this... or easy! It feels like it's going to die at any minute as you pull out of junctions, you can't use any more than minimal throttle opening and need to carefully feather the throttle to keep the engine from bogging completely. Moderation of the choke makes no difference to the way it runs at this time either.
Once half way back (about 2.5 miles) I stopped again where I knew I could safely wait if it died completely and that's when I took this video. As you can see, my little red spark tester flashes away on the far bank. There are NO signs of any spark tracking or leakage visible anywhere in the dark... I even remembered to check for vacuum in the fuel tank and pooped the cap - nothing. Fuel pump was still ticking normally and the glass bowl in the engine bay was full, so it doesn't look to be fuel starvation...... I have a 2nd coil fitted on the car as an emergency measure, so I switched off and swapped to the 'emergency' coil - but the symptoms were EXACTLY the same. Although it will start easily and at first flick of the key, it WILL NOT run properly - you can see in the video I am opening the throttle wide open and holding it WIDE OPEN and all it'll do is make that strangled gasping noise. It I open the throttle wide when it's cold and before these symptoms present, it would rev to the moon, so SOMETHING is breaking down as it warms up or after a few minutes use.... Checking the spark on cranking with the distributor cap off produces a big fat spark and it still wouldn't earth through the rotor arm when it was displaying these running symptoms....
The only thing I noticed was the drop in intensity of light produced by my spark tester as it revved, or tried to, with theses symptoms and I am now wondering if this is a clue? Could the spark be breaking down? Given what I saw last night I am suspecting the coil.... but it produced exactly the same symptoms on the 2nd emergency coil... I guess it could be TWO dead coils? but the chances? Going through the ignition components that have been replaced so far, it's everything..... literally. It's had new plugs, new insulator extensions, new leads, new cap, new rotor arm, new coil(s), and a new PowerSpark electronic ignition kit!
Irrespective, given that it's still not right
nothing can be excluded from suspicion or examination - you can see why I'm exasperated! Any thoughts, suggestions, experience, comments very welcome! Would you concur that there might be a spark issue? The air temp was cool enough that vapourisation seems highly unlikely, no?
Here's the video - note the spark tester flashing away and my hand where you can see me opening the throttle to wide open and holding it all that time where it's bogging...