After careful disassembly of the carburetor and the removal of all non metallic parts, the carburetor body and all other
metallic parts should be cleaned with solvent, or commercial carburetor cleaner, no longer than 30 minutes. Use compressed
air and soft tag wire to clean internal carburetor passages. To do a proper cleaning job, the welch plugs must be removed
to expose the drilled passages.
NOTE: The nylon check balls used in some diaphragm carburetors are not serviceable. Nylon can be damaged if
subjected to harsh cleaners for prolonged periods.
Examine the throttle lever and shaft, choke lever and shaft, and carburetor body at the bearing points and holes into
which the linkage is fastened, and replace if worn or damaged. Any looseness in these areas can cause dirt to enter the
engine and cause premature wear. If dust seals are present, these should be positioned next to the carburetor body.
Idle and High Speed Mixture Adjusting Screw
Examine the idle mixture needle tip and tapered surface
for damage. The tip and tapered surface of the needle must
not show any wear or damage at all. If either is worn or
damaged, replace the adjusting needle. Tension is
maintained on the screw with a coil spring. Examine and
replace the "O" ring seal if damaged (diag. 40).
Examine the tapered surface of the high speed mixture
needle. If the tapered surface is damaged or shows wear,
replace the needle (non-emissioned). Some Tecumseh
carburetors use serviceable jet main nozzles. These are
identified as being non-metallic.
Fuel Bowl Retaining Nut
The retaining nut contains the transfer passage or metering
jet through which fuel is delivered to the high speed and
idle circuit of the carburetor. If a problem occurs with the
BRASS WASHER (used to protect the
"O" ring from the spring)
ONE-HOLE TYPE TW0-HOLE TYPE
idle circuit, examine the small fuel passage in the annular groove in the retaining (metering) nut. This passage must
be clean for the proper transfer of fuel into the idle metering circuit. Torque retaining nut to 50 in. lbs. (5.65 Nm) when
There are two different types of bowl nuts that are used on adjustable main, float style carburetors. One type has one fuel
metering port at the bottom of the nut, and the other has two fuel inlet ports at the bottom of the nut. This difference
relates to calibration changes to the carburetor and is dependent on the application (diag. 41).
NOTE: DO NOT INTERCHANGE BOWL NUTS.
The fuel inlet ports must be free of any debris to allow proper fuel flow.
Fuel Bowl, Float, Needle and Seat
The float bowl must be free of dirt and corrosion. Clean with solvent or carburetor cleaner.
Examine the float for damage. Check the float hinge bearing surfaces for wear, as well as the tab that contacts the inlet
needle. Replace any damaged or worn parts.
The needle and seat should be replaced if any fuel delivery problems are experienced (flooding or starvation). Sealing
problems with the inlet needle seat may not be visible, so replacement is recommended.
Diaphragms, Pulse Pumps, and Primer Bulbs
Inspect diaphragms, gaskets, and primer bulbs for cracks, tears, hardness or brittleness. Replace if necessary.
To install a new welch plug after cleaning the carburetor,
secure the carburetor in a vise equipped with protective
jaws. Place the welch plug into the receptacle with the
raised portion up. With a punch equal to, or greater than
the size of the plug, merely flatten the plug. Do not dent or
drive the center of the plug below the top surface of the
carburetor. After installation of the welch plug, seal the
outer diameter with finger nail polish or equivalent (diag.
Throttle Shaft and Plate
When reassembling, it is important that the lines or lettering
on the throttle plate are facing out when in the closed
position. Position throttle plate with two lines at 12 and 3
o'clock. If the throttle plate has only one line, the line should
be positioned in the 12 o'clock position on Series 1, 6, 8,
and 9 carburetors, and positioned in the 3 o'clock position
on Series 3 and 4 carburetors (diag. 43 & 44).
Test the operation of the throttle and return spring (if
equipped). If binding occurs, correct by loosening screws
and repositioning throttle plate.
Always use a new screw(s) when reinstalling the throttle
shutter (Tecumseh screws are treated with dry-type
adhesive to secure them in place).
NOTE: NEVER REUSE OLD SCREWS.
Choke Shaft and Plate
The choke plate is inserted into the air horn of the carburetor
in such a position that the flat surface of the choke is
down. Choke plates will operate in either direction. Make
sure it is assembled properly for the engine. Test the
operation of the choke and return spring function if equipped
Always use a new screw(s) when reinstalling the choke
shutter as the screws are treated with dry-type adhesive
to secure them in place.
NOTE: NEVER REUSE OLD SCREWS.
The choke shaft and plate must be in the closed position
prior to tightening the screws. Hard starting may be due to
insufficient choking action because of a misaligned choke
plate. Correct by readjusting the choke plate to close
completely. Note the cut-out position of choke shutter if
Fuel Inlet Fitting
Support the carburetor body with a wood block to avoid
damage to other parts. Use a bench vise or press to install
the fitting squarely. Insert the tip into the carburetor body,
coat the exposed portion of the shank with Loctite grade
A, then press it in until the shoulder contacts the carburetor
High and Low Speed Adjusting Screw, Main Nozzle
When reassembling, position the coil spring on the
adjusting screws, followed by the small brass washer and
the "O" ring seal. Turn the high speed adjustment screw
in approximately one turn into the bowl retainer nut to
make an assembly (diag. 47).
On 2-7 hp. engines that use carburetors which have the
metering rod in the idle circuit (carburetor should rattle when
shaking), make certain that the idle adjustment screw is
installed when the carburetor is in an upright position or
the needle will damage the metering rod, adjustment screw
and carburetor casting.
Some carburetors are of the fixed main type and would
not have a high speed adjusting screw.
Inlet Needle and Seat
On float type carburetors, make sure the seat cavity is
clean. Moisten the seat with oil and insert the seat with
the grooved side down and away from the inlet needle.
Press the seat into the cavity using a flat punch close to
the diameter of the seat, making sure it is firmly seated
The inlet needle hooks onto the float tab by means of a
spring clip. To prevent binding, the long, straight end of the
clip should face the air intake end of the carburetor as
shown (diag. 49).
On diaphragm carburetors the inlet needle and seat
assembly are installed by using a socket to tighten the
assembly until seated.
Needle and Seat Pop-Off Test
To test the pop-off pressure, remove the carburetor from
the engine. Be sure to drain any fuel into an approved
container. Invert the carburetor and remove the float bowl.
Place a drop of an oil based product such as WD-40 on
the tip of the needle valve. Using a commercially available
0-30 psi pump and gauge, attach the pumps hose to the
carburetor inlet. Apply approximately 6 psi or until the
needle pops off the seat. The needle should seat at 1.5 psi
or greater for a minimum of 5 minutes. If the minimum 1.5
psi cannot be maintained for this period of time, then service
to the needle and seat is required.
Reinstall the inlet needle and float into the carburetor. The
long end of the spring or clip on the inlet needle must point
toward the air intake end of the carburetor. If a float
dampening spring is used, reassemble using the following
steps (diag. 50).
RETAINER NUT BRASS WASHER
DRIVE IN UNTIL
SEAT RESTS ON
5/32" FLAT PUNCH
SEATS AT THIS
1. Place the float upside down.
2. Position the spring on the float with the long end around and to the back side of the float's center back tang. The ends
must point toward the choke end of the carburetor. Hook the inlet needle clip on the inside float tang so the clip end
points to the choke end of the carburetor (diag. 50).
3. Place the float, float spring, clip and inlet needle in position between the hinge legs of the carburetor. As the float
assembly nears the hinge legs, wind the outside end of the spring so it goes to the outside of the leg (counterclockwise
looking from the choke end).
4. Install the hinge pin from the opposite hinge leg. The
bowl gasket must be positioned over the end of the
spring (diag. 51).
5. Set the proper float height. See "Float Adjusting
Procedure" in this chapter.
The rivet head on the diaphragm must always face toward
the inlet needle valve. On carburetors with an "F" cast into
the carburetor flange as illustrated, the diaphragm goes
next to the carburetor body. Other diaphragm carburetors
have the gasket located between the diaphragm and
carburetor body. Install the cover retaining screws and
tighten (diag. 52).
Fuel Bowl And Bowl Nut
Whenever a carburetor bowl is removed for service, the
fuel bowl "O" ring must be replaced. For easier installation,
lubricate the "O" ring with a small amount oil.
Install the float bowl by placing the detent portion opposite
of the hinge pin. Make sure the deepest end of the bowl is
opposite of the inlet needle. The bowl has a small dimple
located in the deepest part. The purpose of this dimple is
to minimize the chances of the float sticking to the bottom
of the bowl caused by stale fuel (diag. 53).
On some fixed jet (non-adjustable) and adjustable
carburetors, a fibered washer is required between the
carburetor bowl and the bowl retaining nut.
Occasionally, on engines equipped with the dual system
carburetor, some rich starting conditions have occurred
when the engine is warm. This condition can be corrected
by inserting a non-metallic spacer in the center leg of the
carburetor, as shown (part # XXXXX). This spacer is
designed to reduce the amount of prime charge in the main
nozzle area for better starting under warm engine
conditions. It can only be used on Dual System carburetors
and does not lean out the carburetor mixture. (diag. 54)
This spacer must be reinstalled if originally equipped in
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Above is a link to a service manual pdf file.. Chapter 4 will describe linkage with photos. Page 24.