Bicycle with assist engine

An engine assisted manually powered vehicle comprised of a body assembly adapted to accommodate at least one rider, a propulsion device for propelling said body, a manual operator for receiving manual force inputted from the rider for driving said propulsion device, a transmission for driving said propulsion device from said manual operator, said manual operator being configured so that the force applied by the rider varies cyclically during a force application mode by the operator from a minimum value to a maximum value and back to a minimum value, an internal combustion engine coupled to transmission for powering said propulsion device for propelling said body assembly, said engine having a control for varying the output of said engine, a force sensor for sensing the force applied by the rider to said manual operator and adapted to control said engine control for varying the power applied by said engine to said propulsion device in relation to the force exerted by the rider on the said manual operator, a drive coupling for coupling said force sensor to said engine control, a brake operator for controlling a brake for braking the movement of said body assembly, and for selectively uncoupling said drive coupling between said force sensor and said engine control upon operation of said brake control.