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 RETAINER NUT SPRING "O" RING HIGH SPEED ADJUSTMENT SCREW BRASS WASHER (used to protect the "O" ring from the spring) 40 ONE-HOLE TYPE TW0-HOLE TYPE FUELMETERING PORT FUEL-INLET PORTS 41 IDLE FUEL TRANSFER PASSAGE.
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 reinstalling.
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.
ASSEMBLY: Welch Plugs: To install a new welch plug after cleaning the carburetor, secure the carburetor in a vice 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. 42).
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 (diag. 45).
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 applicable.
Fuel Inlet Fitting. Support the carburetor body with a wood block to avoid damage to other parts. Use a bench vice 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 body.
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 (diag. 48). 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).
HIGH SPEED ADJUSTMENT SCREW SPRING RETAINER NUT BRASS WASHER "O" RING 47 DRIVE IN UNTIL SEAT RESTS ON BODY SHOULDER
48 INSERT THIS FACE FIRST 49 THROTTLE END OPEN END OF CLIP CLIP LONG END OF CLIP CHOKE END 5/32" FLAT PUNCH SEAT INLET NEEDLE
SEATS AT THIS POINT HINGE PIN INLET SEAT 50 FLOAT SPRING FLOAT
INLET NEEDLE WASHER.
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 (counter-clockwise 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.
Diaphragm Assembly. 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 # 632158). 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 the carburetor.
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Above is a link to a service manual pdf file. Chapter 4 will describe linkage with photos. Page 24.
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