1985 Honda Civic • 186,000 miles

My honda civic stops while driving and that time the heat indicator says 75%,
all the dash board light comes up and I can start the engine agin instantly and it runs with knock.
after few seconds(30s) it runs without problem.
i notice that only happening when engine heat is riching 70% above.
All the spark plugs are replaced. And I put relays to egnition switch because it has loose contacts and wire harness heating problem in key switch.
radiator is also ok and no coolent leak engine tune is better I recently check eco test.
fual consuption is around 15km per liter.
please help me to sort out.
January 9, 2013.

What is the idling speed and does it stall only when accelerator is released, ie slowing down or coming to a stop?
Are the cooling fans working when the temperature reaches 70 %?
Did you check the ECU for trouble codes?

Jan 9, 2013.