Starting System (Prime Start) - Yamaha F50D Servise Manual

Starting system (Prime Start)

To facilitate the starting of a cold engine, a richer air-fuel mixture than normal is required. For this
reason, the Prime Start system has been used in the F50D and FT50C.
When the engine is cold, the fuel is delivered from the fully opened fuel enrichment valve. As a
result, starting of a cold engine is facilitated.
Once the engine starts, the current flows to the Prime Start system and the Prime Start plunger
then gradually closes the fuel enrichment valve. A few minutes after the engine has started, the
Prime Start plunger completely closes the fuel enrichment valve, thus ending the fuel enrichment by
the Prime Start system.
The Prime Start unit attached to carburetor #1 8 operates for cylinders #1 and #2, while the Prime
Start unit attached to carburetor #3 9 operates for cylinders #3 and #4.
7
6
a
:
b
:
c
:
1 Prime Start
2 Intake manifold of the engine
3 Prime Start plunger
4 Fuel enrichment valve
5 To carburetor #2 or #4
6 Carburetor
7 Intake air
8 Prime Start for #1 and #2
9 Prime Start for #3 and #4
8
1
2
9
3
4
5
a Air
b Fuel
c Plunger movement
Fuel system
0
1
2
3
4
#1
5
#2
6
#3
7
8
#4
9
10
A
2-8