Can you see fuel in the filter when it dies? If not, fuel cap vent or filter or pump suspect then. Carb solenoid working freely and battery connections secure? For the clunk, watch over the starter gears for a damaged tooth and ensure the starter itself is mounted securely.

Has plenty of fuel in lines and filter, battery is ok. Don't know what a carb solenoid is?

The carb solenoid is the round thing on the bottom of the carb float bowl with wires coming from it. You MAY not have one but probably do. For a test, the solenoid should make a click when the key is turned on. Even so, remove the solenoid, depress the plunger, wedge a tooth pick beside it and break off. Re-install solenoid and see if the engine will stay running now.

As soon as the engine stops, you need to determine if you have a good spark. You need to see if there is gas to the carb (pull gas line off carb in some safe place)

Walt Conner