7
At high speed operation, the throttle shutter is in a full
open position. The air velocity through the venturi increases
which further lowers the air pressure at the main fuel
discharge port. All discharge ports are supplying fuel as
the adjustment orifices will allow (diag. 3-4).
The fuel pump diaphragm in the carburetor moves up and
down by pressure changes (pulsations) caused by piston
movement. The pulsations are transferred to the pump by
a passage called the impulse channel. The pump
diaphragm moves up drawing fuel into the pump fuel
chamber during a positive pulse, and a negative pulse
moves the diaphragm down forcing fuel out of the fuel
chamber through the inlet needle into the metering
chamber.
FUEL PRIMERS
Primers used on TC engines supply a solid fuel charge to
the carburetor main nozzle (diag. 3-5). Fuel is forced
directly into the carburetor venturi. A choke shaft and
shutter is not needed or used when a primer is used. This
charge of fuel provides the rich mixture necessary to start
the engine.
Below the main nozzle is a one way check valve to prevent
fuel from being drawn back into the fuel chamber when
the primer bulb is released. The check valve also prevents
air from entering the carburetor during normal engine
operation.
COMPONENTS
Intake Air
Fuel
Engine Vacuum
Impulse
3-4
High Speed
3-5
3-6
1. Diaphragm Cover Screw
2. Metering Diaphragm Cover
3. Diaphragm
4. Diaphragm Gasket
5. Metering Lever
6. Metering Lever Screw
7. Metering Lever Pin
8. Metering Lever Spring
9. Inlet Valve Needle
10. Inlet Valve Seat
11. Welch Plug
12. Choke Shaft
13. Choke Shutter Screw
14. Choke Shutter
15. Idle Mixture Screw
16. Idle Speed Screw
8
11
17. Throttle Shaft
18. Throttle Shaft Return Spring
19. Throttle Shutter Screw
20. Throttle Shutter
21. Fuel Fitting
22. Fuel Inlet Screen
23. Pump Diaphragm
24. Pump Cover Gasket
25. Pump Cover
26. Pump Cover Screw
27. Tension Spring
28. Dust Seal
29. Dust Seal Washer
12
13
19
20 22
26
27
29
2
1
3
5
17
18
23
24
25
27
28
21
WALBRO CARBURETOR
7
6
10
16
4
14
15
9
Not For Resale
www.SmallEngineDiscount.com
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