I often recall this hot start issue in the past. And why “it wasn’t a problem in the 60s” as much as now. And like Bob mentioned “maybe today’s gas” IMHO it absolutely has to do with gas/octane. As well as heat and timing. In my early Pontiac days (70s) I ran #16, #48, #62 and #670 high compression iron heads, and found the hard start issues on hot summer days. I also found that while having this issue if I reached in and retarded my timing a couple of degrees the engine would start right up even while hot. The stater is still hot, so, the only thing this would change is the ignition spark happening later. Since high engine heat (hot summer day) low octane (today’s fuel) and timing advance exacerbate preignition, why else would retarding the timing solve the problem, unless it were a preignition event? Try backing off the timing, running higher octane fuel, lower temp thermostat or all of the above. Best of luck, let us know.
