I have a simple engine (non v-tec) 2000 Civic. Starts and runs great when hot, cranks and cranks when cold. It often starts after a bit of cranking and then a shot with the right foot. One time when it was really bad, I took the air cleaner off and gave it a bit of gas in the intake. It then fired right up first turn. So I'm thinking that it is something to do with the cold start mixture richening circuit. Any ideas where to start with that?

Thanks much in advance!

Replace the Engine Coolant Temperature (ECT) Sensor. That should solve the problem.