OK, that gets us a bit further. Now, the next important clue is that you've said it needs to be choked to restart, after it has stopped. If the choke had no therapeutic effects, I'd say the next most likely cause was a temperature-sensitive ignition coil (your engine has breaker points - it was made in 1980, and electronic ignition was fitted from 1983). However if choke is required, it is losing compression or starving for fuel, and doing so after a fixed time interval of 5 minutes. Let's assume for the moment that you didn't make any mistakes when you overhauled the carburetor.
This may mean the problem is temperature-sensitive rather than time-sensitive, which could fit for, say, lack of tappet clearance. Before we start to get desperate and re-do things you've done before you started this thread, I suggest you check the valve clearances. For that 80000 series engine, the required clearances are inlet 0.005"-0.007", exhaust 0.009"-0.011", measured with the engine cold.
