Some other ideas please

[Volvo Canadian]

Wow, tricky. Wait 10 minutes and she is a little reluctant to go. Sounds less and less like an electrical problem. More like fuel or carburators. Starts good when cold too, right? Yeah, something to do with heat (expansion/contraction) which normalizes-out when the engine cools right off again. Could it be something to do with the fuel pump? Breather in your petrol tank?? Or something is loose on the SU's?

[Amazonjulian]

In response to further questions- distributor clamp is tight, carbs are su's and heat shield is in place

[Derek UK]

Once the weather gets cold, like now, it's not a bad idea to drop the jets down a couple of flats, and leave them that way until Spring. When you try and restart after your 10 minute stop, does it help if you give it a bit of choke? Not full, just enough to pull the jets down a fraction. How much choke do you give it after standing in the cold overnight? Could be that it's just running a bit weak.
This just a guess but with your 123, the ignition setting that you've selected might not be the best for your car and checking with a strobe might show a bit too much advance.
In the mean time I think I'd be giving the old dizzy a good service, just in case I wanted to try swapping it back for testing.

[Amazonjulian]

Derek a bit of choke does help on these occasions. From cold in the morning I give it two thirds choke. You may well be right about this but I'm still surprised to get the issue more or less over night though the weather has certainly turned colder.
Cheers

[Amazonjulian]

Update-not sure whether this would contribute to the issues I have been experiencing but got to work yesterday and there was a strong smell of petrol. Lifted the bonnet and the rear carburettor float chamber was spewing out fuel. I have experienced this before and read all of the threads here on the subject. I had already replaced the float valve in both carbs. Anyway took the lid off to have a check and discovered nothing as on previous occasions. However I've had no recurrence of flooding since and the hot starting is miraculously cured! Interesting but it would be good to understand.

[Derek UK]

Sounds as if it was just flooding out then, even though it didn't usually quite get to the overflow stage. Raw fuel gets into the manifold and then down into the engine. That doesn't ignite well! If it happens again, just put the accelerator pedal to the floor and leave it there while you give the starter a good churn. That's the classic way of clearing any flooding. After a bit, bring the pedal up slowly with the starter still running and it should catch.
You might like to get the carb float tops on the bench and carefully check to see if the floats are sticking at all. No little burrs or misalignment, correct float settings, both the same etc. Don't know if you have brass or the later plastic ones they should both be the same type. Can't say which are best but the plastic ones are obviously cheaper to make. Check them for leaks.

[Volvo Canadian]

Congrats! You might want to replace your fuel filter too, as my guess is you got something in there. My (electric) fuel pump went awhile ago, and after replacing it, had the same problem. In the end (......) I found a tiny sliver of metal stuck in the rubber seal on the top of the float actuator (?). TINY. Got it out, put her all together (again....) and off to Vancouver! I replaced both filters (before and after the fuel pump).

I'm pretty sure you said the bowls were clean, but it does sound like that piece was sticking. If it happens again, could burn your car down!