Starting problem

[Chevyman680063]

For some reason I have problems starting my truck if say I go somewhere like the gas station or store and the truck is turned off for only 5 minutes or so. It turns over but won't start right away. It will eventually start after several tries. If the truck sits for only a minute or less or 10 minutes or more it doesn't have any problem starting up though...just if it sits for around 5 minutes. It has been doing this for at least a year and I'm not sure what's causing it. The motor is a GM Goodwrench 350 (hasn't been modified), the carb is an Edelbrock 600cfm with electric choke, and it has the matching Edelbrock mechanical fuel pump. Any help would be appreciated.