Electromotive force plays a central role in turbulent dynamo mechanisms and carries important information on the nature of the helical turbulent fields. An analysis method is proposed for the electromotive force to evaluate the transport coefficients for the alpha effect and the turbulent diffusivity directly from the measurements. The method is applied to a magnetic cloud event observed by the Helios-2 spacecraft in the inner heliosphere. The electromotive force is enhanced together with the magnetic cloud event by one order of magnitude or two, suggesting that the magnetic field may be amplified in the heliosphere for a short time. Relation between the helicity quantities and the electromotive force is discussed on the basis of the observation.