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In closed evaporation control systems, the purging air flow through the active carbon canister is mixed with the intake air flow. In order to avoid degradation of the λ control and the pollution emission levels, the purged hydrocarbons must be evenly distributed among the cylinders and mixed as thoroughly as possible with the intake air. Based on the purge charactisctics of standard carbon canisters and on the HC levels in a fully charged carbon canister, and using a 4-cylinder sixteen-valve engine, the operating frequency of the canister purge valve and the inlet point of the purge flow into the intake manifold were varied, using n-butane as the hydrocarbon. The measurements taken for HC emissions and the voltages of the lambda probes in the exhaust manifold showed that the inlet point, the valve operating frequency and the microdosing behavior of the valve significantly affect mixture and engine's HC emissions.