Carburetor Troubleshooting

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    Cold StartingProblem

    . . . . . . .CONDITION POSSIBLE CAUSE CORRECTION

    Engine cranks but willnot start. 1) Choke not closing. 1) Inspect choke adjustment andfor something binding. Adjust ifnecessary.

    2) Choke linkagebinding.

    2) Lube with WD-40 and checkfor something bent. Adjust ifnecessary.

    3) No gas in carb. 3) Check fuel delivery. Look forplugged filter or clogged lines,bad pump, stuck needle & seat,and fuel pressure.

    4) Accelerator pumpdefective or blown out.

    4) Replace the pump. Problem isusually caused by bad gas, dirtin gas, or vacuum leak or ignitionproblems causing enginespitback.

    5) No spark or engineproblems such as badcompression.

    5) Diagnose & correct theproblem.

    Engine starts, then dies

    within a few seconds.

    1) Choke not closing

    properly.

    1) See notes above. Adjust

    choke if necessary.

    2) Big vacuum leak onengine somewhere.

    2) Use vacuum gauge to check.Fix the leak. You may have putthe base gasket on wrong or it isthe wrong one for this carb &engine combination.

    3) Choke pull off settingincorrect.

    3) Adjust to factory specs. Carbcan get bumped in shipping ortransportation and canaccidentally change the setting.

    4) Fast idle RPM settoo slow.

    4) Adjust to recommended RPM.

    5)Low fuel delivery. 5) Correct delivery to carb.Usually it is a plugged up filter.

    6) Electrical or 6) Do complete tune up &

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    compression problemson the engine.

    diagnosis. Fix the problemsfound.

    7) Float level set verylow.

    7) Check & adjust the float levelto factory specs.

    8) No electricity up toidle solenoid, or noground.

    8) Check for power & ground.Correct the problem.

    9) Defective idlesolenoid.

    9) Replace it.

    Engine normally startsOK but then dies backingout the driveway or atthe first stop sign. After

    that it runs OK.

    1) Choke not set tightenough.

    1) Set choke a little tighter & tryit.

    2) Choke pull-off

    opening too much.

    2) The setting varies depending

    upon the exact application. Onecarb may fit several applications.Set the pull-off so the choke is alittle tighter.

    Engine starts OK,increases RPM then getstoo slow with lots ofblack smoke.

    1) Choke set too tight. 1) Adjust a little (1/8") looser.

    2) Pull-off set too tight. 2) Adjust so it is open a littlemore.

    3) Slow flooding. 3) Fix cause of flooding. (see"flooding" section coming soon)

    4) Float level very high. 4) (Rare) Set to factory specs.

    5) Power valve blown.(only happens on Ford& Holley)

    5) Replace the power valve.

    6) Pull-off diaphramblown.

    6) Caused by installer allowingengine to spit-back up throughcarb. Replace the pull off.

    7) (on Carter) Pumpblown out

    7) Same cause as #6 above.Replace the pump.

    8) Sunk float. 8) Same cause as #6 above.Replace the float.

    9) Choke spring maybe backwards and isgetting tight when

    9) Remove choke cover, cool offchoke, reverse spring, reinstallcover and set tension to factory

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    heating up instead ofloose.

    specs.

    Engine starts, then racesfor a few seconds and

    then dies every time.

    1) Big vacuum leaksomewhere.

    1) Correct the vacuum leak.Make sure you haven't forgotten

    to hook up a hose somewhere.Base gasket may be wrong oneor on wrong.

    Warm StartingProblem

    . . . . . . .

    CONDITION POSSIBLE CAUSE CORRECTIONEngine cranks butwill not start.

    1) Carburetorflooding.

    1) See section on "flooding" for details onhow to correct.

    2) Choke is closedwhen engine is hot.

    2) Find & fix cause for choke stayingclosed. Look for no heat source, spring inbackwards, or something jammed or bent.

    3) No spark. 3) Do complete tune up.

    4) No compression. 4) Diagnose cause of no compression &fix.

    5) No fuel 5) Check fuel delivery volume andpressure. Look for clogged lines, filter, orpump. Check for kinked or swollen fuellines.

    6) No air. 6) Check for clogged air filter, especially

    after driving through muddy or dusty area.

    7) Too much air 7) Look for big vacuum leak, such asbroken hose, blown gasket, bad powerbrake diaphram, bad PCV valve.

    Engine starts, thendies within a few

    1) Choke is stayingclosed

    1) Diagnose and fix choke problem.

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    seconds. 2) Flooding 2) See section on flooding.

    3) Power valveblown.

    3) Replace power valve.

    4) Venting systemfailure. 4) Check out entire fuel system ventingsystem, inluding the vent valve on thecarb, the charcoal canister, all hoses &check valves in the system, and anysolenoids that trigger the vent system tooperate.

    5) Idle jet pluggedup with dirt.

    5) Clean out the idle jet and any other dirtin the carb.

    6) Idle air bleedplugged up or

    missing.

    6) Check idle air bleed. Clean or replaceas necessary.

    7) Idle cut-offsolenoid notworking.

    7) Check idle solenoid, especially forpower to it and ground to it, replacesolenoid if necessary.

    Engine starts, thenraces for a fewseconds and thendies.

    1) Big vacuum leaksomewhere.

    1) Find the vacuum leak & fix it. Also lookfor wrong base gasket or one that isinstalled wrong. If engine has been spittingback, it may have blown out the basegasket or a gasket in the carb.

    Engine starts OK,but then get realrough. Lots ofblack smoke.

    1) Power valveblown out byspitback up throughcarb.

    1) Replace the power valve.

    2) Slow flooding. 2) See flooding section.

    3) Float sunk.(usually caused byspitback up throughcarb.)

    3) Replace float.

    4) Venting systemproblem.

    4) Check entire venting system & fix.

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    Cold EngineDrivabilityProblem

    . . . . . . .

    CONDITION POSSIBLE CAUSE CORRECTIONEngine stalls whentransmission is put intogear.

    1) Incorrect choke pull-offadjustment.

    1) Readjust the pull-off orreplace if necessary.

    2) Fast idle RPMincorrect (too slow)

    2) Speed up the fast idle tofactory specs.

    3) Engine running toolean because of vacuum

    leak or dirty jet.

    3) Check for vacuum leak.Flow test carb to check jetting.

    Hesitation, stalling,stumbling, flatspot, ordeadspot duringacceleration: Backfiringor spitback up throughcarb.

    1) Vacuum leak. 1) Check for vacuum leak &fix it.

    2) Ignition timing retardedtoo far.

    2) Reset timing.

    3) Accelerator pumpnozzle has dirt in it.

    3) Clean out the nozzle tip.

    4) Accelerator pump cup

    swollen up from contactwith bad gas orchemicals.

    4) Replace the pump cup.

    5) Economizer jet toosmall or partly blocked.

    5) Clean out economizer jet &check the size.

    6) Choke pull-off opentoo far.

    6) Adjust the pull-off tighter.

    7) Secondary throttleplates not closing all the

    way.

    7) Fix it.

    8) Vacuum hoses hookedup wrong.

    8) Connect up right. Beespecially careful of the EGR& Dist. connections:sometimes the pipe locationsare reversed on Rochesters.

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    9) Idle jet partly blockedwith dirt.

    9) Clean out the jet & anyother dirt that is in there.

    10) Distributor timing notadvancing properly.

    (worn breaker plate, wornshaft, pin hole indiaphram, crack in hose,etc.)

    10) Check distributor and allrelated systems carefully.

    Replace defective parts.

    Hesitation, deadspot orstalling after first mile ofwarmup.

    1) Defective electricassist on choke

    1) Replace it.

    2) Defective acceleratorpump (low output).

    2) Replace it.

    3) Float level setting very

    low.

    3) Adjust to factory specs.

    4) Bad ignitioncondenser.

    4) Replace it.

    Periodic backfiring withblack exhaust smoke:Deadspot, flatspot,hesitation, stumbling,backfiring.

    1) Plugged heatcrossover system inmanifold.

    1) Inspect and cleanpassages in intake manifoldand heads. Test heat riservalve, replace if defective.

    2) Defective source of hotair up to the carburetor.

    2) Check and replace asnecessary: heat shroud duct,

    temperature sensor, vacuumdoor motor, manifold vacuumsupply.

    Warm EngineDrivability

    Problem

    . . . . . . .

    CONDITION POSSIBLE CAUSE CORRECTIONHesitation under 1) Vacuum leak 1) Inspect hoses. Route and lead the

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    light throttle:Deadspot &stumble.

    somewhere, orhose off or hookedto wrong vacuumfitting.

    hoses correctly. Look for leak because ofwrong base gasket or it was installedupside down.

    2) Acceleratorpump problems.

    2) Inspect and adjust pump stroke, pumpplunger, discharge nozzles and checkvalves. Inspect the accelerator pump, lookfor swollen pump cup.

    3) Float level setvery low.

    3) Set float to factory specs.

    4) Ignition timingretarded.

    4) Set to factory specs. Make sureadvancing correctly.

    5) Dirty idle jet or

    economizer jet.

    5) Inspect idle jets. Clean as necessary.

    6) Idle speed settoo fast & mixture istoo lean(common!).

    6) Richen up the idle mixture, reset idlespeed to factory specs, then lastly resetthe mixture using the lean drop method.

    7) Idle cut-offsolenoid notworking, or nopower to it or noground to it.

    7) Inspect & fix as necessary.

    8) Frozen orbinding heated airinlet (stuck in fullhot or full coldposition).

    8) Inspect & fix as necessary.

    9) EGR valve stuckon or coming ontoo early (hose onwrong?)

    9) Inspect hose routing to EGR valve &inspect valve. Replace as necessary.

    Doggy, runs rough,lots of black smokeat idle.

    1) Choke stayingclosed or partlyclosed.

    1) Fix choke or heat source.

    2) Slow flooding. 2) See flooding section.

    3) Power valveblown (caused by

    3) Replace power valve.

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    engine spittingback.)

    4) No electricity orheat source to

    choke.

    4) Fix cause of no heat source orelectricity to choke.

    Hesitation underheavy throttle:Deadspot &stumbles. Maybackfire orspitback.

    1) Defectiveaccelerator pump.

    1) Look for dirt in pump nozzles, swollencup from bad gas, or check ball missing orstuck.

    2) Metering rods orpower valvesticking or binding.

    2) Inspect and correct.

    3) Vacuum leak. 3) Locate leak and correct.

    4) Float levelsetting very low. 4) Reset to factory specs.

    5) Plugged up fuelfilter, defective fuelpump, or swollen orkinked lines.

    5) Inspect and replace parts as necessary.

    6) Secondary airvalve set wrong.

    6) Check & adjust the secondary air valvespring.

    7) Ignition timing

    retarded.

    7) Set to factory specs. Check for proper

    advancing.Dies coming up to astop sign, but idlesok.

    1) Bad ormisadjusted BCDD(if equipped).

    1) Adjust to specs and replace it.

    2) Bad throttlepositioner or badvacuum source toit.

    2) Check throttle positioner with a vacuumpump. Replace if defective. Replace anycracked hoses. Make certain that thevacuum hose is connected to the correctpipe on carb or on the thermal switch.Make sure all related pipes have vacuum.

    3) Idle speed andmixture incorrectlyadjusted.

    3) Reset to specs using Recarbco'smethod. See the adjustment andinstallation instructions on our website.

    4) Loose ordefective float pin.

    4) Fix or replace the pin.

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    Poor

    Performance orGas Mileage

    . . . . . . .

    CONDITION POSSIBLE CAUSE CORRECTIONNo power orbad gasmileage.

    1) Plugged exhaust. 1) Check exhaust. Look for plugged catalyticconverter, bad muffler baffle, kinked orcrimped pipe, dirt or other foreign matter inpipe.

    2) Clogged gas tankvent, or fuel ventingsystem.

    2) Remove gas cap & see if performanceimproves. If so clean or replace the gas cap.Check the charcoal cannister, hoses to it &any check valves. Check the electric ventvalve on the carb if there is one, & make sureit is getting power at the right time.

    3) Ignition timingretarded

    3) Check timing at idle and also for fulladvance when revved up. Look for bad orloose hose, hose hooked up to wrong pipe on

    distributor, bad thermal switch, leakingvacuum advance can on the distributor, aworn breaker plate, worn distributor shaft,sticky weights, point gap closed up, etc.

    4) Clogged air filter 4) Replace air filter.

    5) Choke not opening 5) Fix choke or heat source problem.

    6) Secondary notopening.

    6) Check the lockout: secondaries won't openunless choke is coming off all the way. Checkfor sticky or bent shaft or linkage. If air valve

    type (Rochester), check the spring tension,the plastic cam, & metering rods for draggingor sticking.

    7) Wrong main jets orrods

    7) Check them. Replace if necessary.

    8) Dragging brakes. 8) Fix brake problem.

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    9) Low tire pressure. 9) Increase tire pressure at least to factoryrecommendations.

    10) Automatictransmission

    malfunction.

    10) Diagnose & fix automatic transmission.

    11) Wrong ormalfunctioningthermostat in coolingsystem.

    11) Replace thermostat.

    12) Blocked or leakingexhaust heat passagein intake manifold.

    12) Remove manifold & fix it.

    13) Defective

    accessory (powersteering pump, airconditioningcompressor, etc.)causing drag onengine.

    13) Diagnose & repair or replace the

    accessory unit.

    14) Wheels out ofalignment.

    14) Have wheels professionally aligned.

    15) Poor driving habits. 15) Reduce speed, quick acceleration,screeching around corners etc.

    16) Float level muchtoo high, or float partlysunk.

    16) Set to factory recommendations, & checkfloat weight, replace if necessary.

    17) Ignition problems orneeds a tune up.

    17) Do complete tune up & physically inspectthe cap, rotor, wires, coil, plugs, points, etc. inaddition to checking on the scope.

    Flooding . . . . . . .(Note: flooding is gas pouring out uncontrollably, it is NOT hesitation!)

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    CONDITION POSSIBLECAUSE CORRECTION

    Gas pours out whenengine is turned off.

    1) Charcoalcannister is

    saturated with gas.

    1) Replace the charcoal cannister.

    2) Vent valve isnot functioningcorrectly.

    2) Replace the defective valve or fixother cause of it's malfunctioning(like loose connection, etc).

    3) Kinked hoses inventing system.

    3) Replace the kinked hoses withcorrect kind.

    4) Stuck orblocked checkvalves in the vent

    hoses orelsewhere in thesystem.

    4) Replace the check valves.

    5) Gas tank vent isblocked.

    5) Fix it or replace the gas cap ifvent is in the cap.

    6) Gas line locatedtoo close to a heatsource (such as aradiator hose orexhaust manifold).

    6) This causes the fuel to expand &be forced past the needle & seat.Also, fuel can boil in the carb if thereare improper or missing gaskets orspacers between the carb &manifold. A heat riser stuck in theclosed position will also causeboiling and flooding.

    Gas pours out when theengine is running.

    Note 1: often removing thecarb from the manifold &shaking it hard a couple oftimes will effect a cure.

    Note 2: if procedure innote 1 doesn't cure it, theproblems is almost alwaysdirt or bad gas getting intothe carb. Carb will thenneed to be disassembled

    1) Dirt stuck on tipof the needle &seat.

    1) Clean the tip off carefully orreplace the needle & seat and cleanthe entire fuel system out.

    2) Idle speed is settoo fast.

    2) Reduce the idle speed to factoryspecs. If it will not idle slowly, themixture is set too lean, or the idle

    solenoid is not functioning right, orthere is a vacuum leak somewhere(usually not in the carb).

    3) Idle solenoid isnot functioning.

    3) Check for power & ground up tothe solenoid. Check the operation ofthe solenoid. Look for dirt stuck inthe solenoid or the passageways to

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    to fix it. it.

    4) Fuel pumppressure too high.

    4) Check pressure. Use a regulatorto control the pressure or put on anew pump (don't use high pressure

    type).

    5) Fuel pressure isfluctuating or"pulsing" (commonon Colts,Mitsubishi & otherChrysler imports).

    5) Control pulsing with a regulator.

    6) Float is heavy orsunk.

    6) Replace float. Is often caused byspit-back up through carb.

    7) Gas is verygummy, old, or hastoo much alcoholor other chemicalsin it.

    7) Clean bad gas out of carb. Cleanout of fuel system. Use only goodquality gas.

    8) Sugar in thegas.

    8) Clean out the entire fuel system.

    9) Choke notworking.

    9) Check cause of choke failure,choke pull-off failure, or loss of heatto the choke.

    10) Needle notseated properlyduring initial fill.

    10) Try tapping the fuel inlet orneedle & seat area with the handleof a screwdriver. If this doesn'twork, unbolt carb from manifold andshake it hard a couple of times.

    11) On Mikunicarb, the overturnball fell out ofplace.

    11) This is caused by the carb beingoverturned or turned on its side.Remove top and reinstall the ball.

    12) On carbs withexternallyadjustable floatlevels.

    12) Excessive adjustments havecaused the seal to break. Replacethe seals.

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    Hesitation

    DuringAcceleration

    . . . . . . .

    CONDITION POSSIBLE CAUSE CORRECTIONEngine stalls whentransmission is put intogear.

    1) Incorrect choke pull-offadjustment.

    1) Readjust the pull-off orreplace if necessary.

    2) Fast idle RPM

    incorrect (too slow)

    2) Speed up the fast idle to

    factory specs.

    3) Engine running toolean because of vacuumleak or dirty jet.

    3) Check for vacuum leak.Flow test carb to check jetting.

    Hesitation, stalling,stumbling, flatspot, ordeadspot duringacceleration: Backfiringor spitback up through

    carb.

    1) Vacuum leak. 1) Check for vacuum leak &fix it.

    2) Ignition timing retardedtoo far.

    2) Reset timing.

    3) Accelerator pumpnozzle has dirt in it.

    3) Clean out the nozzle tip.

    4) Accelerator pump cupswollen up from contactwith bad gas orchemicals.

    4) Replace the pump cup.

    5) Economizer jet toosmall or partly blocked.

    5) Clean out economizer jet &check the size.

    6) Choke pull-off open

    too far.

    6) Adjust the pull-off tighter.

    7) Secondary throttleplates not closing all theway.

    7) Fix it.

    8) Vacuum hoses hookedup wrong.

    8) Connect up right. Beespecially careful of the EGR

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    & Dist. connections:sometimes the pipe locationsare reversed on Rochesters.

    9) Idle jet partly blocked

    with dirt.

    9) Clean out the jet & any

    other dirt that is in there.

    10) Distributor timing notadvancing properly.(worn breaker plate, wornshaft, pin hole indiaphram, crack in hose,etc.)

    10) Check distributor and allrelated systems carefully.Replace defective parts.

    Hesitation, deadspot orstalling that only seemsto occur after the first

    mile of warmup.

    1) Defective electricassist on choke

    1) Replace it.

    2) Defective acceleratorpump (low output).

    2) Replace it.

    3) Float level setting verylow.

    3) Adjust to factory specs.

    4) Bad ignitioncondenser.

    4) Replace it.

    5) Plugged heatcrossever system inmanifold.

    5) Inspect and cleanpassages in the intakemanifold and heads. Test heat

    riser valve, replace ifdefective.

    6) Defective source of hotair up to the carburetor.

    6) Check and replace asnecessary: heat shroud duct,temperature sensor, vacuumdoor moter, manifold vacuumsupply.

    7) Defective thermalswitch.

    7) Check all thermal switches,especially those connectedwith the distributor, EGR, &vacuum motors in the aircleaner housing.