Range rover classic engine flooding?

I have an 89 classic 3.5 efi on a flapper, which is an ongoing restoration project, (lot of welding to do), which will run for about 20 minutes idling lovely and then you touch the gas and it cuts out and won't restart. Removing the plugs shows that they are wet with fuel. If I clean them all and dry them off I can get it started again. I have had the ECU repaired recently by Carelect, but it still has the same fault, It has had a new dizzy, Magnacor HT leads and coil, so I know that there is a good spark. If anyone has any ideas, of how I can get it to run reliably on petrol I would be most grateful. It is stored in a container and so I have to get it started and out before I can do any welding.

Starts up fine when cold?

First I'd check coolant temperature sensor. It may have seized and needs to be replaced (less than a tenner in UK, e.g. Paddock's). You can also check whether the cold start injector leaks by removing it and pressurizing the fuel rail by moving the AFM-flap with ignition on.

Check also AFM and its connector. And of course air-leaks.

However, if it floods when warm, it usually is the coolant temp sensor. The next best bet would be then cold start injector leak.

Thanks, will try the sender, its been driving me mad.