One thing to check with hard warm starting is the float valves if you have SU's. I had a similar problem and what was happening is that the valves seemed to "leak down" residual fuel pressure and flooded the engine if left for more than a few minutes.

If I waited an hour it would start, and if I started it right back up when warm it would also start. But run into the grocery store for a few minutes and no go.

I believe I was experimenting with Grose valves about this time as well. Went back to stock float valves and only run one filter before the pump. I seem to remember that having a second filter after the pump can contribute as well.

One of the things that fuel injection takes all the fun out of is fiddling with the carbs. But I don't mind.

Best regards,

-Mario E.