Impulse Fuel Pumps - Tecumseh V-twin Technician's Handbook

Main Nozzle (Emulsion Tube)
Place the main nozzle tension spring into the cavity of
the float bowl. Apply a small amount of oil to the o-ring
on the main nozzle and insert it into the float bowl cavity.
Float Installation
Install the float with a new inlet needle and float hinge
pin onto the float bowl assembly. Carefully push the hinge
pin into the retaining post using a small flat blade
screwdriver. Check the float movement for complete
travel.
NOTE: EMISSIONIZED ENGINES OPERATED WITHIN
THE UNITED STATES MAY HAVE HIGH ATTITUDE
JETS AVAILABLE, CONSULT SERVICE BULLETIN
110 FOR INFORMATION.
Final Checks
Test the inlet needle and seat sealing using Tecumseh
service kit 670340 or a similar pop-off tester. To test the
pop off pressure remove the float bowl, float and inlet
needle. Place a drop of fuel on the seat and reinstall the
needle and float. Hook up the pressure tester and apply
approximately 6-9 PSI of pressure or until the needle
pops off the seat. Slowly release the pressure to not
less than 1 ½ PSI. The needle should seat between
1 ½ - 6 PSI for a minimum of five minutes. If the minimum
1 ½ PSI cannot be maintained the needle and seat will
need to be serviced. (Illust. 3-22)
Fuel Bowl Retaining Bail
The retainer bail must hold adequate pressure on the
float bowl to prevent air or fuel leakage during operation.
When re-installed, the force should be adequate to
securely clamp the bowl to the body of the carburetor. If
damage occurred upon bowl removal replace the bail.

IMPULSE FUEL PUMPS

1 - Body, Impulse
2 - Body, Pump
3 - Cover, Pump
4 - Bearing, Spring
5 - *Valve, Check (2)
6 - *Gasket, Pump Cover
7 - *Diaphragm, Pump (2)
9 - Screw, 1-1/4" (4)
10 - *Spring, Pressure
11 - *Filter, Air
Impulse fuel pumps are externally mounted in the fuel
circuit between the fuel supply and the carburetor. A fuel
pump must be used if the fuel supply outlet is lower than
the bowl inlet. There MUST be a in-line fuel filter installed
prior to the pump to prevent system damage.
Impulse fuel pumps are operated by positive and
negative pressure pulsation in the crankcase, which are
created by the up, and down movement of the piston. A
hose called a pulse line, connects the fuel pump
diaphragm chamber to the crankcase and transmits the
pulses to the pump diaphragm. These impulses actuate
the diaphragm creating the pumping action to lift the
fuel from the fuel tank to the carburetor(s). (Illust. 3-24)
The pump body contains check valves, which open and
close preventing the fuel from going backwards from
the pump.
VALVE CLOSED
3-22
ê
CRANKCASE PRESSURE
á
ATMOSPHERIC PRESSURE ACTING
ON DAMPING DIAPHRAGM
á
FUEL FLOW
10
5
9
CARBURETOR
ATMOSPHERIC
VENT
PULSE LINE
FUEL SUPPLY
TO CRANKCASE
á
ê
SUCTION FUEL FLOW
CRANKCASE SUCTION AND
FLOW DIRECTION DIRECTION
ê
ATMOSPHERIC PRESSURE ATMOSPHERIC PRESSURE
á
CAUSED FUEL FLOW
ACTING ON DAMPING
DIAPHRAGM
11
1
4
7
11
2
8
6
3
3-23
FITTING
VALVE OPEN
DIAPHRAGM
FILTER
AIR BLEED
VALVE
CLOSED
3-24
3-9