COLD ENGINE. HIT STARTER AND HEARD AN EXPLOSION. SOON AFTER SMOKE POURING OUT FROM UNDER HOOD. ENGINE FIRE. CALLED 911 AND WAS ABLE TO PUT OUT FIRE BEFORE ARIVAL OF FD. ENGINE HAD TO BE REPLACED. SUSPECTED DEFECTIVE FUEL REGULATOER THAT ALLOWED GAS FUMES TO ACCUMULATE IN AIR PLENUM. USED LOW MILEAGE ENGINE AS REPLACEMENT. COST FOR REPLACEMENT AND RELATED COMPONENTS $5300.