An automatic carburetor (20) enrichment system that controls the air-fuel mixture during cold start of an engine (10) having a carburetor including a fuel bowl (22) and an induction passage (23), includes a sensor (50) that provides a signal indicative of an engine temperature at engine start, a fuel line (30) connected between the fuel bowl (22) and the induction passage, a solenoid valve (40) disposed in the fuel line, and a controller (10) that receives the signal and sets a duty cycle of the solenoid valve associated with the engine temperature to increase the air-fuel ratio of the air-fuel mixture at engine start. The automatic carburetor enrichment system reduces cranking time during cold start, eliminates the need for driver input during cold start, prevents engine stalling without assistance from the operator during the warm up phase, provides a simpler, more cost effective and reliable carburetor enrichment, provides self-drowning protection without the use of an electronic idle switch and eliminates the risk of engine drowning when the engine is cranked with the choke ON and the ignition switches OFF.