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Intermediate Level Maintenance and Repair

Cleaning Craftsman (Tecumseh) carburetors

Simple float carburetors are found on a variety of equipment including many engines made for Sears by Tecumseh. The basic procedures applies to the float carburetors of other manufacturers as well.

If you have been following the recommended preventive maintenance procedures, this may never be needed. But, face it, you do not! The most important PM that is not likely done by 90 percent of mower owners is to drain the gas at the end of the season. With float type carburetors in particular, the result is a buildup which eventually clogs the very fine passageways in the carburetor. What happens is that the gas in the carburetor bowl gradually evaporates leaving behind the gunk and varnish. New gas then flows in from the fuel tank which then evaporates leaving behind more gunk and varnish, and so on and so on and so on. This eventually, well, gums up the works by interfering with float movement and clogging the precision metering holes. Thus, the need for cleaning. Symptoms include difficulty in starting, flooding, surging, lack of power, difficulty in restarting when hot, etc.

The following procedures are specifically for the common non-adjustable carburetors used on the vast majority of Craftsman mowers manufactured in the last 10 years. Carburetors with adjustments and/or a choke are slightly more complex and may differ in other ways. Refer to a small engine repair book or your engine manual for further information.

Carburetor removal

The carburetor can now be moved to the convenience of your workbench.

WARNING: there is still likely a significant amount of gas inside the float bowl. Initial disassembly at least should be done outside so that you can dispose of this safely. Working outside is advisable in any case as the common carburetor cleaning solvents are both flammable and bad for your health.


Most carburetors on Craftsman mowers are variations on a common float design. Newer mowers tend to have no adjustments and no choke - which greatly simplifies cleaning and adjustment. With respect to adjustment, there is none - it either works or it doesn't. If it doesn't, your cleaning was not thorough enough, some parts need replacement, or the problem is not in the carburetor.

IMPORTANT: Before removing any linkages or springs, make detailed diagrams as to how everything goes together. You will NOT remember this several hours later!!! Reassembling the linkages EXACTLY as your found them is critical to the happiness of your engine.

Turn the carburetor upside-down.

Check the throttle plate for free movement - there should be absolutely no hint of binding or tightness. If there is, then this will need to be disassembled as well and cleaned:

Cleaning the carburetor parts

Use carburetor cleaner and lint free cloths or paper towels to remove all built up brown or green gunk, varnish, and other contamination from the metallic parts. Pay particular attention to the machined passages and metering holes.

WARNING: Carburetor cleaner is both flammable and the fumes are toxic. Do all cleaning away from open flames and outdoors if possible. Wear eye protection. The stuff will also eat plastics including some plastic eyeglass lenses.

Take care where non-metallic parts are still in place as extended contact with harsh solvents may degrade their properties (inlet seat and primer bulb, if present). Low pressure compressed air may be used to blow out passages but only use this on the fuel line from inside the carburetor body - else you may end up with the inlet seat clear across the driveway never to be found again.

DO NOT use wires or metal instruments to clear any of the passages as their size is critical.

The small hole in the hollow bolt on the bottom is most critical. Make sure it is cleaned down to the shiny brass and that this hole is unblocked and fully open:

     _     _
    | |   | |  
    | |   | |  
    | |   |_|  
    | |    _  Hole in nut (approximately .025") - use carburetor cleaner
    | |   | |  and wooden toothpicks to clear it out down to shiny brass.
    | |   | |  DO NOT use metal wires!
   _| | _ | |_
  |    \_/    |

If you are absolutely sure there is no hole in the bolt (some models may forgo this), check further up on the central tube - there may be a tiny hole about 1/2" from the bottom. There has to be a hole somewhere for the gas to be sucked up through the carb!

I first use carburetor cleaner inside and out with cotton swabs to remove all traces of gunk from the inside. Use as many as needed till no more discoloration shows up. Then, use the broken end of a wooden toothpick or popsicle stick to clear the .5 mm diameter hole in the side. In severe cases, this hole may not even be immediately visible due to the varnish and gunk buildup.

If this hole is narrowed or clogged, the engine may start but then die in a few seconds. Gas enters the reservoir in the nut slowly or is forced in by priming but the normal suction cannot replenish it quickly enough.

Fine steel wool may be used on the float hinge pin if it is rough or there is evidence of rust but do not use anything abrasive on any of the other parts. Persistence with carburetor cleaner and cloths or paper towels should prove sufficient.

Inspect the inlet needle and seat. The needle should have sharp uniform edges and no visible damage to the conical tip. Any damage half way down the conical part - where it actually contacts the seat - will result in leakage and flooding. The seat can be removed if damaged by pulling it out with a hooked wire - careful - you do not want to scratch the body! If removed, do not reuse but install a replacement. The new seat goes in groove side first (lubricate with a drop of oil) and can be pressed home with a blunt rod.

If the throttle plate was disassembled, clean these parts with carburetor cleaner. Use a cotton swab to get into the bearing surfaces in the carburetor body.

DO NOT attempt to disassemble the carburetor beyond this point - the pressed in main fuel nozzle is precisely fitted and is not removable. The welch plug (pressed in disk) should not be removed unless you suspect contamination in the primer chamber (if any).

Carburetor rebuild kits are available and are economical where almost any parts need replacement.

(From: Jim Williamson (Willjim@gte.net).)

If soaking the carburetor in cleaner:

When you remove each part from the dip tank rinse it with warm/hot water (as hot as your hands can reasonably stand). The parts that have passages - force water through the passage. This does two things: (1) rinses the internal passage of the cleaner and any old junk (2) gives you a VISUAL check that water is coming out the other end of the passage. The visual check is the key here - you could use compressed air to rinse the passages but you don't see the exit stream. On a clean passage the exit stream will be nice and solid indicating no particles hanging up in the passage.

Now as for the hot water - this is to help dry the parts off - evaporation. Sometimes once I've rinsed the parts off I'll use compressed air to further dry the passages - or at least manually blowing through them.

Critical considerations for proper operation


Once all parts have been cleaned and inspected - replaced where needed, proceed as follows:

If you removed the throttle assembly:

Confirm that the throttle plate moves freely between a fully closed and fully open position - there should be no hint of binding or stiffness.

Now for the main event:

You can test for proper operation using low pressure compressed air (i.e., by blowing into the fuel hose), or water or gas. Water is safest but you must make sure to dry everything thoroughly before final assembly. To do this, temporarily reassemble the bowl with the hex head bolt. With the carburetor upright, dribble water into the fuel hose until it accepts no more - perhaps an ounce or two. There should be no leakage - the level of water in the hose should not change at all once it stops. If there is any leakage, there is still a problem with the inlet needle or seat - or the float is gas-logged.

Carburetor installation

With the carburetor positioned in its approximate location on the engine:

Throttle/speed control linkages on Craftsman/Tecumseh engines

The following is for one model! NOT ALL ENGINES ARE SET UP THE SAME! It is best to consult your engine manual. Getting it wrong is not something you really want to do! :(

The user speed control (if any) pulls on a spring which is attached to the 2nd hole from the top on the governor lever. For engines with no speed control, there is a fixed plate or tang to which the spring is attached. Some amount of adjustment is possible by bending this plate.

The carburetor throttle plate has several holes in it. The one that is probably used is that closest to the little cutout (which I can't show with ASCII art) and the tip of the throttle plate return spring. You can probably confirm this by looking for which hole has the paint worn off!

                     __                              _
          Open <-- /    \ --> Close                 | |
                  |o=========.               ,=======o| Top hole
                   \ O   /    '============='       | |
                     \_/ Carburetor   +-- ===========o| Next hole
             _           Throttle     |             | |
            |o|          Plate        +-straight-+  | |
            | |                                  |  | |
            |o=====o---/\/\/\/\/\/o========== ---+  | |
            | |           Spring                    | |
           | O |                                    | |
         Speed Control                              | |
         or Fixed Tang                    Governor  |_|
        (linkages may cross)                 Lever | O |

See: Neil's Tecumseh Throttle and Carburetor Linkage Page for some slightly better diagrams. :)

Initial tests

Add a small amount of gas to the fuel tank - perhaps half a glass or so. Just enough to assure that it will reach the carburetor even if the mower is slightly tilted or jostled.

Inspect around the fuel hose and carburetor body for fuel leaks. If gas starts dripping from the air inlet or anywhere else, there is still a problem with the inlet needle and seat. Disassembly will be required.

Only a few seconds are needed for the gas to fill the carburetor bowl.

Assuming there are no leaks, install the air filter and reattach the spark plug wire or reinstall the spark plug. Attempt the normal starting procedure - prime if recommended.

The engine should start on the first pull! Immediately move the throttle selector to LOW if you have this option. Confirm immediately that it stabilizes at a reasonable speed - stop it quickly if it sounds like the mower is preparing for takeoff - your governor connections are incorrect or binding. If it runs at a fast speed with the speed selector set at LOW, the governor spring is probably in the wrong hole. Check it.

Listen and feel for any significant unevenness, surging, or other unusual behavior. Stop the mower, wait a few seconds, and restart. It should restart with a single pull without priming.

Mow for a few minutes. Stop the engine and confirm that it restarts without priming. Listen and feel for any indication of lack of power or other unusual behavior.

Go take a dinner break. Then confirm that the engine will now start - priming may be needed since it will now be cold.

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