Disclosed herein is a variable spring force intake valve for use in two- or four-stroke internal combustion engines. The device comprises an intake valve body and a torsion spring attached to a gear and rod assembly. Manipulation, via manual or automated means, of the gear and rod assembly adjusts the tension/torsion force exerted by the torsion spring to preload the intake valve and/or to hold the intake valve in the closed position. Varying the tension/torsion force results in an ability to control the timing and the degree to which the ports of the intake valve are actually opened during the operating cycle of the piston, thereby providing a user with an opportunity to enhance the operation of a two- or four-stroke internal combustion engine.