Fuel system of internal combustion engine

In an internal combustion engine having a housing which includes a cylinder head, an exhaust manifold positioned adjacent one side of the engine housing, and an intake manifold spaced from said exhaust manifold and positioned adjacent the other side of said engine housing, comprising the improvement wherein a first carburetor is provided on one side of the engine directly adjacent the exhaust manifold, an intake passage connected between the outlet of said first carburetor and said intake manifold, said intake passage having a first part thereof disposed on said one side of the engine and at least partially covered by said exhaust manifold to create a hot spot so that the fuel-air mixture from the first carburetor is heated by the waste heat from the exhaust gases in the exhaust manifold, said intake passage also having a second part extending between said first part and said intake manifold, said second part being disposed within and extending across said cylinder head for permitting additional heating of the fuel-air mixture from the first carburetor by the waste heat from the cylinder head prior to said mixture being introduced into the intake manifold, a second carburetor provided on the other side of the engine in widely spaced relationship from both said first carburetor and said exhaust manifold, said second carburetor being positioned directly adjacent and having the discharge thereof connected to the intake manifold for supplying a cool fuel-air mixture thereto, and control means for interlocked operation of the throttle valves associated with the first and second carburetors, said control means being operable only subsequent to the opening of the throttle valve associated with the first carburetor.