How did anyone setup the 90 second delay for water pump when the engine is turned off?

This just seems like a smart idea....

Even better, control it entirely using temperature. Ideally, you'd have a variable power controller that runs the pump faster as the water temp goes up, and simply goes off completely below a set temp (say, 120dF). However, the electronics for this aren't all that simple. Such controllers are out there, though.

A simple on/off control with some set temp (say, 140dF) will also work, and is very easy to design and build (a thermistor, one op-amp, one pot, a cap, and a relay). This way, if you fire up the car to just move it out of the driveway, the water pump won't run for 90sec after shutoff each time.

A simple timing circuit will do exactly what you want. I yahoo searched "timer circuit" and the following came up,,,,

http://www.electronickits.com/kit/complete...elec/ck1614.htm

Maybe this will work for you.

Not necessary, after engine shutoff convection currents will still circulate coolant until the thermostat closes. I think what would be more useful would be a small thermostatic-controlled fan on the engine lid to circulate cool air over the carburetor and intake manifold. This keeps the carburetor from getting 'heat soaked' after engine is shut off, or prolonged sitting still at idle.