Service Dealer’s and Technician’s Training and Informational Series
Carburetor Identification, Troubleshooting and Service
Introduction 1
This troubleshooting book is designed as a quick reference for carburetion problems and an aid in identifying failures and their possible causes. It also directs the user to other publications and printed material that assist in properly resolving problems or making adjustments not related to carburetion but could affect carburetion.
Engine Troubleshooting 1
When troubleshooting a carburetor, other areas such as valves, fuel tank venting or gaskets should not be overlooked. The carburetor is dependent on the proper operation of the engine to do its job. The first step in troubleshooting is to determine if you have a carburetor or an engine problem.
Fuel Recommendations 2
Tecumseh Power strongly recommends the use of fresh clean unleaded regular gasoline in all engines. Unleaded gasoline burns cleaner, extends engine life and promotes better starting by reducing build-up of combustion chamber deposits. Reformulated fuels containing no more than 10% Ethanol, 15% MTBE, 15% ETBE or premium gasoline can be used if unleaded regular gasoline is not available. Leaded fuel may be used in countries where unleaded fuel is not available. NEVER USE FUEL CONTAINING METHANOL.
Storage 2
Draining the Fuel System
Gasoline can become unstable in less than 30 days and form deposits that can impede proper fuel flow and engine operation. To prevent deposits from forming, all gasoline must be removed from the fuel tank and the carburetor. An acceptable alternative to removing all gasoline is adding a fuel stabilizer such as Tecumseh Power Ultra-Fresh part number 730245 to the gasoline. Fuel stabilizer should be added to the fuel tank or storage container. Always follow the mix ratio found on the stabilizer container. Run the engine at least 10 minutes after adding the stabilizer to allow it to reach the carburetor.
Oil Cylinder Bore
High Altitude Jet for Emissionized Carburetors 3
The following list of altitude compensation jets is being provided for use with emission grade carburetors at elevations between 6,000 and 11,000 feet (1,824 - 3,344 meters).
High Altitude Carburetor Kits for Fixed Main Carburetors 4
This list applies only to products built prior to emissions regulation. Engines which are identified as compliant with CARB (California Air Resources Board) or EPA (US Environmental Protection Agency) regulations can NOT be changed from their factory setting unless specifically authorized.
Engines built to O.E.M. specifications may experience starting and operating problems when used in areas where the altitude is 4,000 feet (1220 meters) above sea level or higher. A leaner fuel/air mixture is desirable at higher elevations to sustain good engine startability and operating characteristics. Engines built with adjustable idle and main circuit carburetors can be adjusted to optimize performance.
The following will assist you in selecting the correct high altitude/leaner jetted bowl nut for engines equipped with fixed main or dual system carburetors. Order parts from your Authorized Tecumseh Power Distributor or Dealer.
Throttle Control Brackets, Governors, and RPM Adjustments 5
Before adjusting any mixture screws, reset the screws to the recommended carburetor presets. Check for proper governor adjustments as outlined in the appropriate Technician's Handbook. Identify the locations of your high speed and low speed RPM adjustment screws. Check to make sure that the throttle control brackets are adjusted properly to allow for full choke. Always make sure that normal maintenance procedures (ie., oil, fuel, air cleaner, etc.) have been checked. Consult microfiche card #30, the computer parts look up system or Service Bulletin #107 for C.P.S.C. specifications to determine the proper RPM settings. Start the engine, allow it to warm up, the carburetor can then be adjusted for optimum performance by using the information outlined in this book. Now the low and high speed screws can be adjusted to the recommended RPM's.
How to Identify a Tecumseh Power Carburetor 5 - 10
TecumsehPower has a variety of carburetors. To help identify these carburetors here are some simple procedures to follow.
DUAL SYSTEM CARBURETORS
The easiest way to identify the dual system carburetor is by the presence of a large primer bulb located on the side of the carburetor. The absence of adjustment needles help to identify the carb as well. The dual system carburetor is used on 4-cycle vertical crankshaft rotary mower engines.
SERIES 1 CARBURETORS
Series 1 carburetors come in a variety of styles. They are used on both 2 and 4-cycle vertical and horizontal shaft engines in the 2 through 7 h.p. range. It is a float style carburetor with a smaller venturi than the Series 3 and 4 carburetors. Some will have an adjustable idle and main and others will have a fixed main with an adjustable idle. There are also some fixed speed applications that will only have a fixed main system and the idle system will not be drilled.
SERIES 1 EMISSION
This carburetor is similar to the standard Series 1 carburetor. The emission equivalent has a fixed idle and main. The idle restrictor jet will be capped to prevent access unless the cap is removed. The fixed main jet is part of the bowl nut. A ball plug is visible from the bottom, which seals the passage. This carburetor also has a serviceable main nozzle emulsion tube.
SERIES 2 CARBURETORS
Series 2 carburetors were used on outboard engines. This carburetor is the same as the Series 1 with the exception of the remote adjustable idle mixture screw, and a built in fuel pump.
Series 2 carburetors have a built-in fuel pump consisting of a fuel pump element which inflates and deflates with crankcase pulsations which opens and closes two flap valves in the fuel pump, thereby pumping fuel from a remote tank to the carburetor float bowl.
When replacing the fuel pump element, install with the slot opening at a 45 angle as illustrated. Installation in any other position will damage the diaphragm.
SERIES 3 & SERIES 4 CARBURETORS
Series 3 and 4 carburetors are generally used on 8 through 12.5 horsepower 4-cycle engines. The venturi size of these carburetors are larger than Series 1 and Dual System Carburetors. The quickest way to identify these carburetors is by the presence of bosses on each side of the idle mixture screw.
SERIES 3 & SERIES 4 EMISSION
This carburetor is similar to the standard Series 3 & 4 carburetor with a few subtle differences. The emission equivalent has a fixed idle and main. The idle restrictor jet will be capped to prevent access unless the cap is removed. The fixed main jet is part of the bowl nut. A ball plug is visible from the bottom, which seals the passage. This carburetor also has a serviceable main nozzle emulsion tube.
VECTOR CARBURETORS
The Vector carburetor is a float feed, nonadjustable carburetor, with a one piece extruded aluminum body. The float bowl, float, nozzle, and venturi are nonmetallic, which eliminates the corrosion and varnishing problems associated with similar metallic parts. Common service areas of the carburetor are contained in the fuel bowl, which include the float, needle, seat and main nozzle emulsion tube. All of these parts can be serviced without removing the carburetor body from the engine.
SERIES 6 CARBURETORS - 4 CYCLE
Series 6 carburetors are used on 2 and 4-cycle engines. They have a larger venturi than the dual system carburetor and use a simple fixed idle system. Series 6 carburetors used on both vertical and horizontal applications are nonadjustable. The 4-cycle version pictured has a stepped primer bulb.
SERIES 6 CARBURETORS - 2-CYCLE
Series 6 carburetors used on TVS/TVXL840 engines are similar in appearance and operation to the carburetors used on 4-cycle engines.
SERIES 7 CARBURETORS (EMISSION)
The Series 7 carburetor is an emissions grade carburetor used on medium frame vertical shaft overhead valve engines. It has a non-metallic bowl and a snap-on bowl retainer to connect it to the carburetor body. This model has a fixed main jet and a fixed idle jet; both are located in the carburetor bowl. The float bowl, float, nozzle, and venturi are non-metallic, which eliminates the corrosion and varnishing problems associated with similar metallic parts. Common service areas of the carburetor are contained in the fuel bowl, which include the float, needle, seat and main nozzle emulsion tube. All of these parts can be serviced without removing the carburetor body from the engine.
SERIES 8 CARBURETOR (EMISSION)
The Series 8 carburetor has both a fixed main and idle circuit. The fixed idle system is achieved by a restrictor jet that meters the fuel for the idle circuit. The idle restrictor jet will be capped to prevent access unless the cap is removed. The fixed main jet is part of the bowl nut. A ball plug is visible from the bottom, which seals the passage. This carburetor also has a serviceable main nozzle emulsion tube. It also has a stepped primer bulb.
SERIES 9 CARBURETOR
The Series 9 carburetor is an emissions carburetor that uses the same carburetor body as the Series 8 but with a simple fixed idle system, identical to the one used on the Series 6 carburetor. It has the idle discharge port located at the 7 o'clock position on the throttle end of the carburetor. Identify this carburetor by the stepped primer bulb, the presence of a non-drilled idle mixing well and a serviceable main nozzle emulsion tube
SERIES 10 (EMISSION)
The Series 10 carburetor is identical to the Series 8 carburetor with the addition of a choke. To assist in cold weather starts. It has a fixed idle and main. The idle restrictor jet will be capped to prevent access unless the cap is removed. The fixed main jet is part of the bowl nut. A ball plug is visible from the bottom, which seals the passage. This carburetor also has a serviceable main nozzle emulsion tube. It also has a stepped primer bulb to assist in starting.
SERIES 11
This carburetor adds a fuel chamber, built into the carburetor body, that feeds fuel into the venturi during the initial warm up period. This patented feature eliminates, hunting, surging and false starts inherent to emissions engines. However external identification of the Series “11” carburetor has been a challenge. To make this ID simple, the Series “11” carburetor idle restrictor cap will be black, and all others will be gray. The part number for the black cap is 640200 and the gray is 640053.
SERIES 11 BRIDGED
This carburetor is identical to the Series “11” with the exception of the center leg. A non-metallic jet is pressed into the center leg to allow additional fuel into the main jet for applications that require this fuel to enhance run performance.
Non-Tecumseh Power Carburetors 10
DELLORTO CARBURETOR
The Dellorto carburetor is similar to the dual system carburetor. It has no adjustments and has a primer assist start. It has a noncorrosive float and the needle is viton tipped, eliminating the viton seat found in the dual system carburetor. The angle of the fuel inlet is adjustable and attached to the carburetor body with a banjo bolt. This carburetor is used on some TVS rotary lawnmower engines.
WALBRO LMK CARBURETOR
The Walbro LMK has a large venturi and a fixed main with an adjustable idle. It is used on some OHV engines. This carburetor has a noncorrosive float and a viton tipped needle. It also has a nonmetallic choke shaft. It is easily identified by the Walbro name on the carburetor body next to the idle adjustment screw.
WALBRO WHG CARBURETOR
The WHG, used on OH cast iron engines, can be built as a fully adjustable, single adjust or nonadjustable carburetor. It has a large venturi. Its most recognizable feature is the large square mounting surface on the choke end of the carburetor.
Diaphragm Carburetors 10 - 11
DIAPHRAGM CARBURETORS
The diaphragm carburetors are unique. These carburetors can be operated at a more severe angle than float style carburetors. They still require that the fuel supply be located in a position that allows it to be gravity fed. Its most distinctive feature is the lack of a fuel bowl.
WTA WALBRO CARBURETOR
The WTA carburetor has a rubber-type diaphragm, which is exposed to intake pressure on one side and to atmospheric pressure on the other. The WTA is used on TC200 and 300 engines. There are two adjustment screws. They are the idle mixture screw and the idle RPM screw. The WTA has a choke and an all metal fuel inlet fitting. The Walbro name is molded onto the pump cover.
WT WALBRO CARBURETOR
The WT Walbro carburetor is used on the TC-II style engine. It is similar to the WTA carburetor but its reverse image. The WT has no choke lever and has a combination plastic and metal fuel inlet fitting.
TILLOTSON HU CARBURETOR
The Tillotson HU carburetor is the reverse image of the WTA Walbro carburetor. It is used on the TC-II. The Tillotson HU has a replaceable main and Tillotson is visible on the pump cover.
Tecumseh Power TC CARBURETOR
This carburetor has a fixed idle and main which meets the emissions standards for two cycle engines. The main jet is serviceable and can be accessed by removing the plastic cap. The jet is removed for cleaning purposes only, and must be covered after servicing to maintain compliance with emissions regulations.
Carburetor Cleaning Series 8 - 11 - 12 - 16
Emission Carburetors 17
The following information will help you better identify some of the common components of emission grade carburetors. Emission carburetors will be internally vented. On the Series 7, 8, 9, 10, 11 and 11 Bridged the atmospheric vent hole is increased in size from earlier model carburetors. This passage way leads to the atmospheric vent chamber which is double vented into the bowl cavity. This double venting is common on emissions grade carburetors.
Pre-Sets and Adjustments (Non-Emission) 18 - 20
RPM ADJUSTMENTS
GOVERNED / NON-GOVERNED IDLE
WALBRO CARBURETORS 4 CYCLE PRE-SETS AND ADJUSTMENTS
MAIN AND IDLE PRE-SETS
WALBRO CARBURETORS 2-CYCLE PRE-SETS AND ADJUSTMENTS
TILLOTSON CARBURETOR 2-CYCLE PRE-SETS AND ADJUSTMENTS
IDLE PRE-SET
FINAL ADJUSTMENT
WALBRO CARBURETORS 4-CYCLE FIXED (WHG) (OH120 - 180)
Troubleshooting Carburetion Chart 21 - 22
TROUBLESHOOTING CARBURETION
Tecumseh Power CARBURETORS FLOAT AND DIAPHRAGM
Use the troubleshooting chart to determine the cause of a particular carburetor problem. Once the problem is identified, it will be necessary to select the proper corrective action.
Troubleshooting Tecumseh Power Carburetors 23
FUEL SYSTEM
EMISSION
AIR SYSTEM
DIAPHRAGM SYSTEM
Troubleshooting Carburetion TC Series Chart 24 - 25
ADJUSTMENTS
FUEL SYSTEM
AIR SYSTEM
METERING SYSTEM
LEVER
SPRING
DIAPHRAGM
INLET NEEDLE & SEAT
NOZZLE CHECK VALVE
Troubleshooting Walbro WTA, WT and Tillotson HU 26
The Walbro and Tillotson diaphragm pump carburetors operate similarly by using a diaphragm impulse fuel pump and a diaphragm / needle metering system. The most common problems associated with these carburetors will be found in these two areas.
Metering System 26
Service Carburetor Information 27 - 28
To identify a carburetor for replacement on an engine, use the model and specification number of the engine. If the engine model and specification number are not present for some reason, there is a model and code date number stamped on the body of every carburetor.
With the model number, you will be able to find all of the information needed to repair or replace the carburetor. In the Master Parts Manual or the microfiche carburetor section, locate the manufacturing to service number cross reference list. Find the service part number listed for the carburetor. It will also list the page or grid where the carburetor breakdown can be found.
When referencing the carburetor in the price list, the original carburetor may be superseded to a service carburetor. Some Tecumseh Power service carburetors will not have the fuel fitting. These carburetors can be identified by the description listed as SVC Carb NF, meaning service carburetor, no fitting. If this designation is not made in the listing, the carburetor will have a fuel fitting.
When the price list supersedes the original carburetor you are ordering to a service carburetor, you will need to identify the parts not included on the service carburetor. To determine these parts, turn to Division 5, Section A in the Master Parts Manual or the appropriate microfiche card listed under "carburetor." The information can be found under the title "List of parts required to build a complete carburetor from a standard service carburetor."
The cross section shown below uses 631211 as the original carburetor number. The price list supersedes that number to 631790A which is a service carburetor. The items shown following the number must be added to the service carburetor to make it a complete carburetor. Parts may be used from the original carburetor if they are in good condition. NEVER REUSE THE ORIGINAL THROTTLE AND CHOKE SHUTTER SCREWS.
Using the Computer Parts Look Up System 29
Computer parts look up systems are fast, efficient and allow you to use several different options when looking up parts. If you know the part or manufacturing number of the carburetor you can use that number to access information to provide you with a parts list, artwork, availability and pricing. One method of obtaining the carburetor part number requires you to know the engine model number. This is not always available and could cause your customer some inconvenience having to return home to retrieve that information from the engine. If the customer has the carburetor along, you simply need to locate the manufacturing number on the carburetor and enter that number into the look up system. The following steps will direct you through the procedures needed to use either parts look up system.
Float Adjustment Procedure 29
FLOAT HEIGHT SETTINGS
Proper float setting will require the use of Tecumseh Power tool part number 670377 or a 11/64" drill bit. The procedure for setting the float height is as follows. Remove the bowl gasket, then hold the carburetor in the inverted position. Place the tool across the carburetor body opposite and parallel to the float hinge pin. Adjust the float height by bending the tab on the float until it touches.
Carburetor Service Tips 30 - 33
SERVICING THE SEAT
INSTALLING INLET NEEDLE & FLOAT
INSTALLING THE FLOAT BOWL
FLOAT BOWL SERVICE - VECTOR AND SERIES 7
ASSEMBLY OF MAIN MIXTURE SCREW
REMOVAL AND INSTALLATION OF WELCH PLUGS
FUEL INLET FITTING
INLET FITTING REMOVAL
PROPER INSTALLATION OF CHOKE AND THROTTLE PLATES
THROTTLE PLATE SERVICE
DIAPHRAGM CARBURETOR "F" DESIGNATION
SERVICEABLE EMULSION TUBES
VECTOR AND SERIES 7 EMULSION TUBE SPRING
HOT RESTART
Primer Bulb Service 34
PRIMER BULB IDENTIFICATION
Care must be used when replacing carburetor primer bulbs. Using the wrong primer bulb could cause hard starting or non-starting problems. Currently, Tecumseh Power uses four different carburetor mounted primer bulbs. To avoid problems, use the Master Parts Manual for the correct application. The five primer bulbs currently used feature two different shapes; derby and stepped (or hourglass) and two different venting types; internal or external.
STEPPED PRIMER BULBS
A stepped primer bulb is used to force a charge of air into the bowl through the atmospheric vent chamber. The sealing surface as pictured prevents air from going back into the air filter.
Fuel Filters 35
FUEL TANK FILTERS
Tecumseh Power engines use some form of filtration prior to the carburetor. When a non-Tecumseh Power tank is used, an in- line fuel filter between the tank and carburetor is required. The filters use a 75 micron fibrous paper to trap even the smallest particles of dirt while maintaining the same flow rate. An arrow showing the direction of flow is molded into the body of the filter to aid in installation.
All fuel tanks provided by Tecumseh Power have a 75 micron stainless steel filter screen molded right into the tank over the fuel outlet. On TC series engines, a fuel filter is located on the fuel line in the tank. These filters can become restricted when foreign debris enters the tank or when varnish and gum deposits form due to stale fuel. Be sure to check these areas if you have a fuel flow problem.
Internal Atmospheric Vent Passage 35
Failure Analysis 36 - 38
WORN THROTTLE AND CHOKE SHAFTS
When operating in a dirty or sandy environment, these areas can wear rapidly causing erratic performance. Some shafts have been plated and dust shields have been added to retard this wear. This is done based on the application needs. Keeping these areas free from dirt and grit will extend the life of the carburetor.
CRUSHED FLOAT
A crushed float will sink to the bottom of the carburetor bowl holding the inlet valve open and causing the engine to flood. This condition is caused either from water in the fuel bowl freezing during extreme cold temperatures or by blowing compressed air directly into the fuel inlet while the carburetor is assembled.
WORN HINGE PIN
The hinge or hinge pin can wear excessively from dirt or foreign matter in the fuel system. These worn areas will cause a sticky or binding float which will result in either a flooded or starved engine.
WORN NEEDLE AND SEAT
This is another area that can wear rapidly from dirt or foreign matter in the fuel system. This condition creates a poor seal at the seat area causing the carburetor to flood or the engine to run rich. This can also cause the needle to stick in the seat which will stop the flow of fuel.
WORN CARBURETOR BODY
If throttle shafts are plated, operation in a dirty or sandy environment will tend to cause wear to the carburetor body in the shaft area. Excessive wear in this area will cause erratic engine performance or a binding throttle plate. Again, to avoid this situation, clean these areas regularly and keep them free from dirt and grit.
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