Well now naturally with a thread title as it is I had in mind what I wanted to try....
But I'm not married to that being the problem. I've got some time between flights here, let me see if I can answer some of these good troubleshooting tips:
Al - no, I've never tried to use the starter in those two instances. The "problem" doesn't take long to develop - it is more or less instantaneous once the car is shut off while good and hot. For instance, in a recent 1.5 hour race with 5 min pit stop the car wouldn't restart and I had to get pushed out of the pits. I will try it though this weekend if we still have the problem, which I assume we will.
Sandy - we've tried starting fluid in an attempt to get it get it fired up while hot and it didn't help. When really cold out, like 25-30F, it likes a bit of starting fluid to get fired up.
Jac Mac - we don't run coolant through the manifold, blocked all that stuff off and to the carbs too. And I added a nice heat shield earlier in the year to keep the carbs from getting heated up and to help a bit with keeping the manifold cool. IR thermo says it helps. Also put on new cap and rotor a couple of times last year as well as plugs in attempts to make sure the ignition system was good. Always had spark for this issue, big and fat from the MSD.
Russ - haven't tried the bucket of cold water! We've used jump start batteries before on the system to no avail.
I think Jac Mac is right as it must be air/fuel related in some way. Maybe my most recent change to some air filters that actually pass air will have something to do with it, but as you know you can always fit a theory to your observations as you hope for a solution.....lets see, cold car, bad filters, rich mixture, starts easily when cold out......hot car, air filters won't pass air worth a damn, too rich a mixture, no starting......
Fun thread as I wait for plane number two in DC, thanks for all the ideas too...