Cleaning Carburator

8/17/2019 Cleaning Carburator

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Cleaning Carburettors

Simple foat carburetors are ound on a variety o equipment including manyengines made or Sears by Tecumseh. The basic procedures apply to the foatcarburettors o other manuacturers as well.

I you have been ollowing the recommended preventive maintenanceprocedures, this may never be needed. But, ace it, you do not! The mostimportant that is not li"ely done by #$ percent o vehicle owners is to drainthe gas at the end o the season. %ith foat type carburetors in particular, theresult is a build&up which eventually clogs the very 'ne passageways in thecarburetor. %hat happens is that the gas in the carburetor bowl graduallyevaporates leaving behind the gun" and varnish. (ew gas then fown in rom theuel tan" which then evaporates leaving behind more gun" and varnish, and soon and so on and so on. This eventually, well, gums up the wor"s by intereringwith foat movement and clogging the precision metering holes. Thus, the needor cleaning. Symptoms include di)culty in starting, fooding, surging, lac" o

power, di)culty in restarting when hot, etc.

The ollowing procedures are speci'cally or the common non&ad*ustablecarburetors. +arburetors with ad*ustments andor a cho"e are slightly morecomple- and may dier in other ways. /eer to a small engine repair boo" oryour engine manual or urther inormation.

Carburetor removal

• 0rain the uel, close the shuto valve i any, or remove the gastan". 1n the common 2ehicles, the tan" either slips o or is astened with

a couple o screws. The gas line should pull right o. Inspect the uel lineor damage or crac"ing and replace it i these are severe.

• /emove the air 'lter, inspect, and set aside. The small plastic

enclosed air 'lters twist o countercloc"wise. I it is clogged and o thepaper type, replacement will be needed. I it has a oam element, this canbe reused i it doesn3t all apart. /emove the oam element, clean in soapor detergent and water, dry, and then coat it with a ew drops o reshengine oil. %or" the oam with your 'ngers to distribute the oil. 4or othertypes, see your engine manual.

• 5se a large screwdriver to loosen the two screws astening theinta"e maniold to the cylinder bloc". I the gas"et separates easily andcleanly, then it can be reused though a dab o non&hardening sealer isadvisable once you have tested the vehicle to be sure that your newlyrestored carburetor is unctioning properly. I it tears or is damaged in anyway, then it should be replaced. I the bolts are really tight, an open endwrench may be o help but common soc"ets may not 't around thebottom bolt. Thin walled soc"ets may wor".

• 0isconnect the throttle lin"age and governor spring noting which

holes they go in. I1/T6(T7 I you get this screwed up you could have a


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runaway situation on your hands when you go to restart it. This candestroy the engine in a ew seconds!

• 0isconnect the rubber tube rom the primer bulb, i any. It shouldpull o. I it tears near the end, there is probably enough slac" so that a

new tube is not required.

• 0isconnect the speed control and stop switch wire, i any. (ote howthey are installed. The carburetor can now be moved to the convenience o your wor"bench.

%6/(I(87 there is still li"ely a signi'cant amount o gas inside the foatbowl. Initial disassembly at least should be done outside so that you candispose o this saely. %or"ing outside is advisable in any case as thecommon carburetor cleaning solvents are both fammable and bad or

your health.

Disassembly

ost carburetors on 2ehicles are variations on a common foat design.(ewer vehicles tend to have no ad*ustments and no cho"e & which greatlysimpli'es cleaning and ad*ustment. %ith respect to ad*ustment, there isnone & it either wor"s or it doesn3t. I it doesn3t, your cleaning was notthorough enough, some parts need replacement, or the problem is not inthe carburetor.

I1/T6(T7 Beore removing any lin"ages or springs, ma"e detaileddiagrams as to how everything goes together. 9ou will (1T remember thisseveral hours later!!! /eassembling the lin"ages :;6+T(ote7 there is probably a dimple in the bottom o the bowl in the lowerlevel side. This is normal and probably there to "eep the foat o o the

bottom where gun" and varnish collect because you didn3t drain the gas.?


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• The foat will now be visible. /otate it to the ully up position. Theinlet needle will come up with the hinged part o the foat. It is held inplace by a wire clip but will now be ree. The inlet needle is actually a oursided metal rod with a polished conical tip. /emove the needle and clip.

• 5se a pair o needle&nose pliers to pull out the hinge pin which willree the foat. +areul & the foat is made o relatively thin brass and issusceptible to damage. +hec" the throttle plate or ree movement & thereshould be absolutely no hint o binding or tightness. I there is, then thiswill need to be disassembled as well and cleaned.

• 5se an open&end wrench to loosen the inta"e pipe and then removethe nuts and bolts. The maniold will probably come ree with the gas"etintact. 0on3t lose the metal strip to which the governor spring attaches.+hec" or dirt and other debris and set aside.

• 5se a @A straight blade screwdriver to remove the screw in thecenter o the throttle plate. (ote the position o the hole in the plate andthe orientation o the plate. >The hole should be toward the engine sidewith the carburetor body upright. ar" it beore removal i in doubt.?

• Tap the carburetor i needed to remove the throttle plate.

• ull the throttle shat out o the carburetor body. Ta"e care not to

lose the spring with the elt andor metal washer. (ote their positions.

Cleaning the carburetor parts

5se carburetor cleaner and lint ree cloths or paper towels to remove allbuilt up brown or green gun", varnish, and other contamination rom themetallic parts. ay particular attention to the machined passages andmetering holes.

%6/(I(87 +arburetor cleaner is both fammable and the umes are to-ic.0o all cleaning away rom open fames and outdoors i possible. %ear eyeprotection. The stu will also eat plastics including some plastic eyeglass

lenses.

Ta"e care where non&metallic parts are still in place as e-tended contactwith harsh solvents may degrade their properties >inlet seat and primerbulb, i present?.


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The small hole in the hollow bolt on the bottom is most critical. a"e sureit is cleaned down to the shiny brass and that this hole is unbloc"ed andully open7

I you are absolutely sure there is no hole in the bolt >some models may

orgo this?, chec" urther up on the central tube & there may be a tiny holeabout @D rom the bottom. There has to be a hole somewhere or the gasto be suc"ed up through the carb!

I 'rst use carburetor cleaner inside and out with cotton swabs to removeall traces o gun" rom the inside. 5se as many as needed till no morediscoloration shows up. Then, use the bro"en end o a wooden toothpic"or opsicle stic" to clear the .E mm diameter hole in the side. In severecases, this hole may not even be immediately visible due to the varnishand gun" build&up.

I this hole is narrowed or clogged, the engine may start but then die in aew seconds. 8as enters the reservoir in the nut slowly or is orced in bypriming but the normal suction cannot replenish it quic"ly enough.4ine steel wool may be used on the foat hinge pin i it is rough or there isevidence o rust but do not use anything abrasive on any o the otherparts. ersistence with carburetor cleaner and cloths or paper towelsshould prove su)cient.

Inspect the inlet needle and seat. The needle should have sharp uniormedges and no visible damage to the conical tip. 6ny damage hal way

down the conical part & where it actually contacts the seat & will result inlea"age and fooding. The seat can be removed i damaged by pulling itout with a hoo"ed wire & careul & you do not want to scratch the body! I removed, do not reuse but install a replacement. The new seat goes ingroove side 'rst >lubricate with a drop o oil? and can be pressed homewith a blunt rod.

I the throttle plate was disassembled, clean these parts with carburetorcleaner. 5se a cotton swab to get into the bearing suraces in thecarburetor body.

01 (1T attempt to disassemble the carburetor beyond this point & thepressed in main uel noCCle is precisely 'tted and is not removable. The%elch plug >pressed in dis"? should not be removed unless you suspectcontamination in the primer chamber >i any?.

I soa"ing the carburetor in cleaner7%hen you remove each part rom the dip tan" rinse it with warmhotwater >as hot as your hands can reasonably stand?. The parts that havepassages & orce water through the passage.

This does two things7 >@? rinses the internal passage o the cleaner andany old *un" >D? gives you a 2IS56< chec" that water is coming out the


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other end o the passage. The visual chec" is the "ey here & you could usecompressed air to rinse the passages but you don3t see the e-it stream.1n a clean passage the e-it stream will be nice and solid indicating noparticles hanging up in the passage.

(ow as or the hot water & this is to help dry the parts o & evaporation.Sometimes once I3ve rinsed the parts o I3ll use compressed air to urtherdry the passages & or at least manually blowing through them.

Critical considerations for proper operation

• The inlet needle and seat must be in good condition or else thecarburetor will food due to lea"age or result in erratic operation due touneven gas fow. I there is any evidence o damage, these parts will needreplacement. The F edges o the needle should not be worn >the

sharpness would change about DG o the way rom the pointed end?. I the edges are noticeable rounded, replace the needle. There may bevarnish deposits on the needle, rubber seat, and the metal casing in whichit is installed. These must be totally removed using carburetor cleaner andsot >wooden or plastic? tools.

• The foat height ad*ustment should be airly accurate. %ith the foat

and inlet needle reinstalled >and the seat replaced i it was removed?,invert the carburetor & the foat should sit *ust about horiContal. 4or moreprecision, a .D@$ >HF? drill bit should *ust 't between the body and thenon&hinge end o the foat.

• The machined passages must be ree and clear and not damaged &ever use wires to clean them. 5se compressed air, carburetor cleaner,wooden stic"s, etc. owever, do ma"e sure that they are ully open. Thereare no blind passages in these carburetors so a strong light should permityou to see that they are unbloc"ed >the ollowing are typical & your modelmay dier slightly?7

o 6ir bleed, inlet side angled down toward main *et.

o assage to primer chamber, inlet side.o Slot towards center at edge o welch plug >may not be present?.

o air o main uel passages in central cylinder in main body.o ain metering hole in bowl bolt.

• The hole in the bowl bolt is the main metering ori'ce and it is criticalto the proper operation o the carburetor. This area also tends to collect alot o crud. It will yield to repeated use o carburetor cleaner, cotton swabs>J&tips?, and wooden stic"s. +ontinue cleaning until you are down to shinybrass. Kust don3t become impatient and use any wires or sharp tools tospeed the process!

• 6ny primer should be air&tight or it to unction properly and or the

engine to run properly. 6ny lea"s will result the primer being partially or


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totally ineective. In addition, the engine will run rich and contaminantsmay enter the carburetor. +hec" or damaged rubber parts or hoses thathave allen o.

I the primer bulb is on the carburetor, there is a 3%elch plug3 >a metal dis"

pressed into a mating cavity? sealing the primer chamber. 1n the sidetoward the center, there is a tiny rectangular hole that must be open & itoten gets clogged and may not even be readily apparent. 0o not attemptto remove the %elch plug unless you seriously suspect something isinside. I pressing the primer bulb results in a blast o air out o the hole,it3s probably 'ne. %here the primer is separate rom the carburetor, thereis usually no welch plug.

• The foat must be air >and gas? tight. Sha"e it & i there is any gasinside, the foat will need replacement. >It3s possible there may be metal

particles or other debris sealed inside at the time o manuacture & this willcause no harm.? ut the foat under water & there should be absolutely noevidence o bubbles and lea"age. inholes sometimes develop in the thinbrass and while these can be soldered, this practice is not recommended.

• The large 1&ring must seal properly. I it lea"s, the engine will run

rich and contaminants may enter the carburetor bowl. /eplacement isusually recommended whenever the carburetor is disassembled. owever,i it is in perect condition, you can try to reuse ma"ing sure that themating suraces are clean and smooth. 5se some engine oil on the 1&ringto assure a tight seal.

(ote7 %hen tightening the foat bowel, ta"e care that the 1&ring doesn3tget pinched or "in"ed resulting in an inadequate seal or no seal. 6 narrowstic" may be useul to help it along. I the carburetor hasn3t been removedrom the engine, a mirror will be needed to inspect it.

Reassembly

1nce all parts have been cleaned and inspected & replaced where needed,proceed as ollows7I you removed the throttle assembly7

• /einstall the throttle shat along with its spring and elt andor metalwasher. oo" the spring onto the ridge on the carburetor body. a"e sureit moves reely. 01 (1T lubricate.

• 6ttach the throttle plate to the shat with the original screw. a"esure the plate is correct side out and that the hole is positioned on theright acing the upright carburetor rom the throttle plate side. 6s youtighten the screw, slightly rotate the throttle shat to allow the plate toseat properly & *iggle it a bit at the same time. %hen properly installed,

the plate itsel limits the return movement o the throttle. It should be ullyclosed at this point.


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+on'rm that the throttle plate moves reely between a ully closed andully open position & there should be no hint o binding or stiness.

• /eattach the air inlet pipe with gas"et using the two sets o nuts and

bolts. 0on3t orget the metal strip or the governor spring i yourcarburetor uses this. Tighten securely & F to L t&lbs i you use a torquewrench.

(ow or the main event7

• Install a new seat i you removed the old one. The new seat goes ingroove side 'rst >lubricate with a drop o oil? and can be pressed homewith a blunt rod.

• Install the foat using the hinge pin.

• Insert the inlet needle hoo"ing the retaining clip on the tab near thefoat hinge. +hec" or ree movement o the foat.

• %ith the carburetor body inverted, chec" the foat heightad*ustment. It should seat almost horiContally. 4or a more precise test, usea $.D@$ >HF? drill bit as a gauge across the outer ring o the carburetorbody & the foat should *ust touch this. Bend the tab on the foat to ad*ust.>(ote7 unless you replaced some parts, this setting will probably be 'ne.?

9ou can test or proper operation using low pressure compressed air >i.e.,by blowing into the uel hose?, or water or gas. %ater is saest but youmust ma"e sure to dry everything thoroughly beore 'nal assembly. To dothis, temporarily reassemble the bowl with the he- head bolt. %ith thecarburetor upright, dribble water into the uel hose until it accepts nomore & perhaps an ounce or two. There should be no lea"age & the level o water in the hose should not change at all once it stops. I there is anylea"age, there is still a problem with the inlet needle or seat & or the foatis gas&logged.

• Install the large 1&ring around the carburetor body. 5se a small

amount o engine oil to aid in assuring a good seal.

• lace the bowl over this assembly ma"ing sure that it does not pinchthe 1&ring. 1rient it so that the deep part is almost opposite the foathinge >it should actually point directly away rom the engine when thecarburetor is mounted.?

• Install the he- head bowl bolt and 'ber washer. Tighten securely>one Tecumseh service manual lists E$ inch&pounds, but others have norecommended torque or this bolt?. +65TI1(7 I3ve heard o people

brea"ing the bolt by either attempting to loosen it the wrong way or overtightening upon reassembly to stop lea"s. I gas lea"s out in the area o


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the bolt head, the 'bre washer may be missing or damaged. 4or testing atleast, a non&hardening gasoline resistant sealer li"e 4orm&6&8as"et B>tm?can be used.

Carburetor installation

%ith the carburetor positioned in its appro-imate location on the engine7

• /einstall the throttle and governor lin"ages %here there is no speedad*ustment or idle position, the direct governor lin"age goes in the holeclosest to the engine and the spring hoo"s onto a '-ed vertical metal stripwith only one hole at one end and the lower hole in the governor lever atthe other. Thus, in operation, the spring attempts to "eep the throttleopen and the governor pulls on the throttle to close it. Increased springtension results in higher speed.

• /eattach the primer tube, i any.

• /eattach the stop switch wire, i any.

• Install the carburetor onto the engine with a new gas"et i needed.

• 0ouble&chec" that the throttle lin"age and governor spring are inthe proper holes and nothing is binding & you should be able to move thethrottle bac" and orth without any stic"ing or tightness. It should returnto the ull countercloc"wise position instantly as a result o the governorspring tension.

• 0o not replace the air 'lter at this time.

• /einstall any throttle selector or cable. +on'rm that it operatesproperly & usually ST1,

Cleaning Carburator

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