Mariner Mercury 105/140 JET, Service Manual

Page: 187 / 797

90-824052R3 JUNE 2002 FUEL SYSTEMS - 3B-27
b. Idle Air Bleed Jets (1 per carb.) - The idle air
bleed jet meters air and is located next to the
back drag vent jet. If a jet with a smaller orifice
is installed the fuel/air ratio becomes richer. If
a jet with a larger orifice is installed, fuel/air
ratio becomes leaner.
c. Air Trim Screws (2 per carb.) - Located
beneath welch plugs and are preset at
factory. DO NOT remove welch plugs and
adjust trim screws.
NOTE: If welch plugs and trim screws are removed
for carburetor cleaning, refer to “IMPORTANT”
preceding.
Off-ldle Circuit Description
Back View
Side View
c
f
a
d
a
d
e
b
50756
a - Carburetor Body
b - Off-Idle Air Jet
c - Off-Idle Discharge Holes
d - Throttle Shutter
e - Off-Idle Tube
f - Back Draft Circuit Port (Port Bore Only)
The off-idle fuel flow circuit is controlled by an off-idle
air jet located in each carburetor bore. Each venturi
has one off-idle tube and one off-idle air jet. The
circuit functions at off-idle speeds until full throttle
operation occurs.
Back Draft Circuit Description
Side View
a
50755
a - Back Draft Jet (Bowl Vent)
The back draft circuit contains a vent jet, located next
to the idle air jet, which supplies less than
atmospheric pressure to the fuel bowl at mid-range
which results in improved fuel economy.
High Speed Fuel Circuit Description
Side View
Front View
c
e
c
f
a
b
a
d
50755
a - Fuel Bowl
b - Main Fuel Jet
c - Main Discharge Tube
d - Float
e - Main Discharge Tube Air Inlet
f - Cross Hole Vents
The high speed fuel flow is controlled by the main
(high speed) jets and are located in the fuel bowl. A
fuel/air mixture is drawn from the fuel bowl thru the
main discharge tubes during full throttle operation.
HIGH SPEED FUEL CIRCUIT ADJUSTMENTS
Main (High Speed) Jet (2 per carb.) - If a jet with a
smaller orifice is installed, the fuel/air ratio becomes
leaner. If a jet with a larger orifice is installed, the ratio
becomes richer.