Just replaced fuel pump as that was diagnosed to be problem but still problem is evident

Something has to be fubar with the main jet circuit of carb. That explains why it starts and then shortly thereafter shuts down. Also explains why when you give it gas it cuts out cold.

U have ignition but NO engine will run without proper fuel flow.

Fuel pump? It might not have enough flow.

sounds like fuel problem ! what bike have you got and is it carb or injectors , is it elec fuel pump or gravity fed and how old is the fuel in the tank ?

sounds like the fuel pump is heating up and failing

HI

It is clearly that you have poor mixture.
Every engine needs more fuel in starting, thats the reason for the choke circuit.
But yours doesnt work as you said
Fix your choke circuit in your carbs and every thing will be OK
If you had problem with your fuel pump your bike never run ok cold or hot it dies in any throtlle response