No hot start update

[Paul Hill]

I recently asked about potential causes of failing to start when hot. The 
guess was a vapor lock caused by a faulty injector cooling fan. I checked 
that and it seems to be fine.
Today I got another data point: I stalled the car when it was hot and it 
refused to start. The engine had only been stopped for 2 or 3 seconds 
(literally) when I tried it and it was totally dead (not misfiring or 
stumbling) . Up till then it was running perfectly: Smooth, powerful, full 
rev range etc.. After 45 minutes I tried it again and it was still dead. I 
pulled a plug lead off and connected it to a spare spark plug which I 
rested on the head. When I turned the engine over there was no spark. I 
jiggled the plug to make sure it was grounding properly, and tried it 
again. At first there was no spark and no running, then after a couple of 
seconds of cranking the engine started and of course the plug was sparking 
away nicely.
So it looks like I'm changing my search from fuel to ignition. What puzzles 
me is why it would go from running perfectly to not starting in seconds. 
Component temperatures can't have changed, so it must be a difference in 
the running versus starting condition.
Any suggestions??

Paul

1986 5KCSTQ