Fuel Pump; Carburetors; Pilot System - TOHATSU NB-1000 Service Manual

SECTION 3
3

Fuel Pump

The fuel pump may be integral with the carburetor or
3
mounted on the side of the crankcase and contains one or
more internal diaphragms (1). The diaphragms move in response to
changing crankcase pressures (2) which draws fuel in (3) and
pumps fuel out (4). A series of check valves (5) in the pump ensure
that fuel moves only in one direction.

Carburetors

The carburetors use a pilot system and main system to meter and
deliver an atomized fuel mixture to the engine for combustion under
varying operating conditions.

Pilot System

The pilot system is a slow speed system consisting of the slow
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jet, slow air jet, pilot outlet, bypass, and pilot adjusting screw.
At 1/4 throttle and less, mixed fuel (1) enters the carburetor and flows
from the carburetor float chamber (2) through passage (3) to the pilot
jet (4). Air (5) measured at the pilot air jet (6) is directed through
passage (7) and combines with the existing fuel from the pilot jet to
form fuel/air mixture (8). After exiting bypass (9), the mixture directly
enters engine (10) or passes pilot adjustment screw (11) for output to
the engine through pilot outlet (12). Unrestricted air flow to the engine
is available through venturi (13).
3-10
T1003
1-/ 2-Cylinder