My moki seized!
I had just started the engine, and was waiting to take off. The engine died and I had to restart it. When I then started to move out on the field it died and I was unable to turn it over.
A few minutes later when I was taking off the spinner it freed up. I disassembled the engine and could find nothing wrong.
I was using 20% FAI fuel. The oil was 1/2 klotz and 1/2 castor. The engine is tightly cowled with its head sticking out the cowl about 1/4 inch. I have had several flights with this aircraft with no troubles.
Any ideas about what caused this?

Set too lean, cowled too tightly or air leak.

I don't understand something here. You say the motor seized, yet you found nothing wrong when you took it apart. A seized engine will always show some piston and ring damage. Because that's what seizes....the piston and ring against the cylinder wall.

If you found no mechanical damage or galling of metal on the piston or vertical scratches on the cylinder, then it didn't seize. You may have had a hydraulic lock from excess fuel when you tried to restart it.

I have a Merco .61 gasoline engine that has seized on several different occasions before I learned to put about four ounces of castor in a gallon of fuel along with the two stroke oil. It never suffered any damage even though it could not be turned for about five minutes. It never seizes with the castor in it.