2008 Suzuki LT-A400/F, LT-F400/F ATV Service Manual, Page 74Get this manual
1A-2 Engine General Information and Diagnosis: Condition Engine idles poorly Possible cause Valve clearance out of adjustmentPoor seating of valvesDefective valve guidesWorn rocker arm or arm shaftDefective generatorDefective CDI unitSpark plug gap too wideDefective ignition coil resulting in weak sparkingFloat-chamber fuel level out of adjustment in carburetorClogged jetDefective fuel valveImproperly set pilot screwValve springs weakenedValve timing out of adjustmentWorn cams or rocker armSpark plug gap too narrowDefective ignition coilFloat-chamber fuel level tool lowClogged air cleaner elementClogged fuel pipe, resulting in inadequate fuel supply to carburetorDefective fuel valveToo much engine oil in the engineWorn piston rings or cylindersWorn valve guidesCylinder wall scored or scuffedWorn valve stemsDefective stem sealsLoss of valve clearanceWeakened valve springsValve timing out of adjustmentWorn piston rings or cylinderPoor seating of valvesFouled spark plugWorn rocker arms or shaftsSpark plug gap incorrectClogged jets in carburetorFloat-chamber fuel level out of adjustmentClogged air cleaner elementToo much engine oilSucking air around intake pipeHeavy carbon deposit on piston crownNot enough oil in the engineDefective oil pump or clogged oil circuitFuel level too low in float chamberAir leak from intake pipeUse of incorrect engine oilCorrectionReference Item AdjustReplaceReplaceReplaceReplaceReplaceAdjust or repairReplaceAdjustCleanReplaceAdjustReplaceAdjustReplaceAdjustReplaceAdjustCleanClean and primeReplaceCheck with inspection window, drain out excess oilReplaceReplaceReplaceReplaceReplaceAdjustReplaceAdjustReplaceRepairClean or replaceReplaceAdjust or replaceCleanAdjustCleanDrain out excess oilRetighten or replaceCleanAdd oilReplace or cleanAdjust Retighten or replaceChange Engine runs poorly in high speed range