Inlet manifold & hot water's exit ( from cylinder head ) are in the same
aluminium block, so inlet manifold cannot be cool : after engine warms
up, intake air & fuel get too hot, i.e. cannot expand much when ignited,
torque slowly drops as engine warms up.
 Hot water piped out from bottom of carburetor gets piped straight back
into cylinder head, so cylinder head gets too hot.  This hot water should
be piped into radiator to be cooled 1st.  Users with infra red thermo
meter / camera can easily see, those w-o can use their fingers to feel,
that this pipe is far hotter than the rubber hose with cooled water from
radiator.
 Even in a cool ambient air of 27°C ( let alone in hotter weather ), non-
believers can glue a few heatsinks onto this pipe, then [i] see ( per gauge
) how much slower the water ( leaving cylinder head ) temperature will
rise, & to a lower maximum  [ii] feel how much torque rises @ once.
 Air intake should be as cool as possible www.circletrack.com/techarticles/1822/
i.e. must not be piped near the hottest parts of engine: e.g. Honda F20A,
Toyota 4A-F 1600E, & Lotus campro correctly have their air intake
piped away from *exhaust manifold & rocker cover.  4G15P has air
piped over * in a black ( this colour absorbs the most heat ) plastic pipe,
its underside ( facing * ) gets very hot.  If user paints this underside to
white / silver, or insulate it against heat from * using e.g. polystyrene,
air intake pipe will be less hot.