I once owned a '64 Corvette that refused to start when warmed up. In fact, Zora-Arkus Duntov was my passenger at a Corvette function in 1979 and the &^%# thing wouldn't start with the "Father of the Corvette" sitting next to me! Something had to be done. I sold the car the next day.
Well, that's neither here nor there. The point is, previously this had been a problem that confounded me. I had changed starters, wiring harnesses, carbs, condensers, ignition switches, etc.
ad nauseum. $$$$$$$$$$$ The engine was still hard to start after shutting down unless I allowed it to cool back down. 'Turns out the problem was the coil all along. For some reason, when it got hot, it wouldn't deliver the necessary spark to start the engine. But if I waited a half hour or so, the engine fired up and ran without any problem, even though the coil must have been warm while driving. I finally changed coils (many dollars later) and that solved the problem. Too late too smart.
You might try temporarily hooking up a known good
six-volt coil and see if that helps. Also, Ernie makes a good point about the condenser. They fail in multiple ways: gradually, suddenly or intermittently. They'll operate fine and then all of a sudden start misfiring. Then they work fine again on their own. Or they suddenly die and won't fire at all. Sometimes they even die overnight just sitting. Model A condensers are strange animals, to be sure. Always carry a spare condenser in your Model A because you just never know what they'll do. After trying a new coil and no change, swap condensers just for grins and giggles.
One more thing to check - and I've posted this story before about what happened to my 1928 Roadster on the German Autobahn in 1974. I won't reprint it here yet again, but I'll cut to the chase. Same scenario: when the engine warmed up and was shut off, it wouldn't start again until the car had sat for a while and cooled down. It was misfiring, too. The problem turned out to be a defective off-shore terminal box. The two stud heads were too big to fit inside their bores on the backside of the box, so just enough of the heads stuck out to arc against the heated firewall, which had expanded. This shorted out the ignition. Once the firewall had cooled down and contracted away from the bolt heads, the engine fired right up. When I removed the terminal box, I could see black splotches on the firewall where the bolt heads had been arcing. You might try loosening the four little bolts that secure the terminal box to the firewall enough to pull the unit out a bit. Shove a piece of cardboard between the terminal box and the firewall to keep it there. See if that makes any difference. If your car was restored in the 1970's or 1980's with the poor quality parts available then, you might have one of these sloppily-made terminal boxes. I have since fixed at least two other Model A's that had the same problem and the same off-shore 1970's terminal boxes. Rick's Antique Auto sold a ton of them and they're still out there somewhere. Maybe in YOUR garage?
Marshall
