The one cold start engine fire I had in a C172 I had them pull the cowl & check it. This was a cold day, rental airplane, and I didn't think it was going to start & suck the flames in so I got out the C02 fire extinguisher. I learned a couple things from the experience:
1) If your airplane has an accelerator pump, don't be pumping the throttle because the excess fuel in the induction system can catch fire!
2) In cold weather prime before you begin your preflight.
-- IFMU