Fuel supply for internal combustion engines

Internal combustion engine comprising intake passage means leading to combustion chamber means and provided with throttle valve means, main carburetor means for providing a supply of air-fuel mixture, starting fuel supply means having starting fuel supply passage means of a cross-sectional area which is small in relation to that of the intake passage means and opening at one end to the intake passage means downstream of the throttle valve means and at the other end to atmosphere, starting fuel discharge means discharging starting fuel into said starting fuel supply passage means so that the fuel discharged from the starting fuel discharge means to the starting fuel supply passage means is mixed with air passing therethrough to form an air-fuel mixture, starting valve means provided in the starting fuel supply passage means downstream of the starting fuel discharge means, said starting valve means being connected with a movable wall defining a vacuum chamber at one side in such a manner that when a negative pressure is introduced to said vacuum chamber said starting valve means is moved to a position where it closes the starting fuel supply passage means, spring means biasing the starting valve means to an open position, means for connecting the vacuum chamber with the intake passage means at engine temperature above a predetermined value, and exhaust passage means connected with said combustion chamber means.