|NotTaR of small Gasoline Engines and Rotary Lawn Mowers : Cleaning Craftsman (Tecumseh) carburetor..
1994-2007, Samuel M. Goldwasser. All Rights Reserved. Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied: 1. This notice is included in its entirety at the beginning. 2. There is no charge except to cover the costs of copying.
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Intermediate Level Maintenance and Repair
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.
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
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.
- Under the bowl is a large hex head bolt. On the non-adjustable carburetor,
this is closed on the bottom. It is also not a simple bolt but includes
the precision main fuel metering hole which will need to be cleaned
thoroughly. Use a proper socket to unscrew this bolt (counterclockwise).
Drain any residual gas from the bowl. CAUTION: I've heard of people breaking
the bolt by either attempting to loosen it the wrong way or overtightening
upon reassembly to stop leaks.
- There is a fiber washer under the bolt. There may also be a fiber washer
on this nut inside the float bowl. Don't lose these or get them mixed up.
Turn the carburetor upside-down.
- Carefully remove the bowl and O-ring. Inspect these for damage. (Note:
there is probably a dimple in the bottom of the bowl in the lower level
side. This is normal and probably there to keep the float off of the
bottom where gunk and varnish collect because you didn't drain the gas.)
- The float will now be visible. Rotate it to the fully up position. The
inlet needle will come up with the hinged part of the float. It is held in
place by a wire clip but will now be free. The inlet needle is actually
a four sided metal rod with a polished conical tip. Remove the needle
- Use a pair of needlenose pliers to pull out the hinge pin which will free
the float. Careful - the float is made of relatively thin brass and is
susceptible to damage.
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:
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
- Use an open-end wrench to loosen the intake pipe and then remove the nuts
and bolts. The manifold will probably come free with the gasket intact.
Don't lose the metal strip to which the governor spring attaches. Check
for dirt and other debris and set aside.
- Use a 1/8" straight blade screwdriver to remove the screw in the center of
the throttle plate. Note the position of the hole in the plate and the
orientation of the plate. (The hole should be toward the engine side with
the carburetor body upright. Mark it before removal if in doubt.)
- Tap the carburetor if needed to remove the throttle plate.
- Pull the throttle shaft out of the carburetor body. Take care not to lose
the spring with the felt and/or metal washer. Note their positions.
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
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
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
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.
Once all parts have been cleaned and inspected - replaced where needed,
proceed as follows:
- The inlet needle and seat must be in good condition or else the carburetor
will flood due to leakage or result in erratic operation due to uneven gas
flow. If there is any evidence of damage, these parts will need replacement.
The 4 edges of the needle should not be worn (the sharpness would change
about 2/3 of the way from the pointed end). If the edges are noticeable
rounded, replace the needle. There may be varnish deposits on the needle,
rubber seat, and the metal casing in which it is installed. These must be
totally removed using carburetor cleaner and soft (wooden or plastic) tools.
- The float height adjustment should be fairly accurate. With the float
and inlet needle reinstalled (and the seat replaced if it was removed),
invert the carburetor - the float should sit just about horizontal. For
more precision, a .210" (#4) drill bit should just fit between the body
and the non-hinge end of the float.
- The machined passages must be free and clear and not damaged - never use
wires to clean them. Use compressed air, carburetor cleaner, wooden sticks,
etc. However, do make sure that they are fully open. There are no blind
passages in these carburetors so a strong light should permit you to see
that they are unblocked (the following are typical - your model may differ
- Air bleed, inlet side angled down toward main jet.
- Passage to primer chamber, inlet side.
- Slot towards center at edge of welch plug (may not be present).
- Pair of main fuel passages in central cylinder in main body.
- Main metering hole in bowl bolt.
- The hole in the bowl bolt is the main metering orifice and it is critical
to the proper operation of the carburetor. This area also tends to collect
a lot of crud. It will yield to repeated use of carburetor cleaner,
cotton swabs (Q-tips), and wooden sticks. Continue cleaning until you are
down to shiny brass. Just don't become impatient and use any wires or
sharp tools to speed the process!
- Any primer should be air-tight for it to function properly and for the
engine to run properly. Any leaks will result the primer being partially
or totally ineffective. In addition, the engine will run rich and
contaminants may enter the carburetor. Check for damaged rubber parts
or hoses that have fallen off.
If the primer bulb is on the carburetor, there is a 'welch
plug' (a metal disk pressed into a mating cavity) sealing the primer
chamber. On the side toward the center, there is a tiny rectangular hole
that must be open - it often gets clogged and may not even be readily
apparent. Do not attempt to remove the welch plug unless you seriously
suspect something is inside. If pressing the primer bulb results in a
blast of air out of the hole, it's probably fine. Where the primer is
separate from the carburetor, there is usually no welch plug.
- The float must be air (and gas) tight. Shake it - if there is any gas
inside, the float will need replacement. (It's possible there may be metal
particles or other debris sealed inside at the time of manufacture - this
will cause no harm.) Put the float under water - there should
be absolutely no evidence of bubbles and leakage. Pinholes sometimes
develop in the thin brass and while these can be soldered, this practice
is not recommended.
- The large O-ring must seal properly. If it leaks, the engine will run
rich and contaminants may enter the carburetor bowl. Replacement is
usually recommended whenever the carburetor is disassembled. However,
if it is in perfect condition, you can try to reuse making sure that
the mating surfaces are clean and smooth. Use some engine oil on the
O-ring to assure a tight seal.
If you removed the throttle assembly:
- Reinstall the throttle shaft along with its spring and felt and/or metal
washer. Hook the spring onto the ridge on the carburetor body. Make sure
it moves freely. DO NOT lubricate.
- Attach the throttle plate to the shaft with the original screw. Make
sure the plate is correct side out and that the hole is positioned on
the right facing the upright carburetor from the throttle plate side. As
you tighten the screw, slightly rotate the throttle shaft to allow the
plate to seat properly - jiggle it a bit at the same time. When properly
installed, the plate itself limits the return movement of the throttle.
It should be fully closed at this point.
Confirm that the throttle plate moves freely between a fully closed and
fully open position - there should be no hint of binding or stiffness.
- Reattach the air inlet pipe with gasket using the two sets of nuts
and bolts. Don't forget the metal strip for the governor spring if your
carburetor uses this. Tighten securely - 4 to 6 ft-lbs if you use a
Now for the main event:
- Install a new seat if you removed the old one. The new seat goes in groove
side first (lubricate with a drop of oil) and can be pressed home with a
- Install the float using the hinge pin.
- Insert the inlet needle hooking the retaining clip on the tab near the
float hinge. Check for free movement of the float.
- With the carburetor body inverted, check the float height adjustment.
It should seat almost horizontally. For a more precise test, use a
0.210" (#4) drill bit as a gauge across the outer ring of the carburetor
body - the float should just touch this. Bend the tab on the float to
adjust. (Note: unless you replaced some parts, this setting will probably
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.
With the carburetor positioned in its approximate location on the engine:
- Install the large O-ring around the carburetor body. Use a small amount
of engine oil to aid in assuring a good seal.
- Place the bowl over this assembly making sure that it does not pinch
the O-ring. Orient it so that the deep part is almost opposite the
float hinge (it should actually point directly away from the engine
when the carburetor is mounted.)
- Install the hex head bowl bolt and fiber washer. Tighten securely (but
there is apparently no recommended torque for this bolt). CAUTION: I've
heard of people breaking the bolt by either attempting to loosen it the
wrong way or overtightening upon reassembly to stop leaks. If gas leaks
out in the area of the bolt head, the fiber washer may be missing or damaged.
For testing at least, a non-hardening gasoline resistant sealer like
Form-A-Gasket B(tm) can be used.
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! :(
- Reinstall the throttle and governor linkages Where there is no speed
adjustment or idle position, the direct governor linkage goes in the hole
closest to the engine and the spring hooks onto a fixed vertical metal
strip with only one hole at one end and the lower hole in the governor
lever at the other. Thus, in operation, the spring attempts to keep the
throttle open and the governor pulls on the throttle to close it. Increased
spring tension results in higher speed. Don't get these backwards when you
go to reinstall the carburetor on the engine!!! See the section:
Throttle/speed control linkages on Craftsman/Tecumseh
- Reattach the primer tube, if any.
- Reattach the stop switch wire, if any.
- Install the carburetor onto the engine with a new gasket if needed.
Tighten securely (6 to 8 ft-lbs).
- Double-check that the throttle linkage and governor spring are in the
proper holes and nothing is binding - you should be able to move the
throttle back and forth without any sticking or tightness. It should
return to the full counterclockwise position instantly as a result of
the governor spring tension.
- Do not replace the air filter at this time.
- Reinstall any throttle selector or cable. Confirm that it operates
properly - usually STOP, LOW, HIGH. STOP should engage the stop switch.
LOW should leave the governor spring tension where it was. HIGH should
increase the governor spring tension slightly. If there is an IDLE
position, the throttle plate should be almost closed.
- Reinstall any trim pieces that were removed.
- Reinstall the fuel tank and fuel hose with clamp, if any. Open the fuel
valve, if any.
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. :)
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
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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