Fuel System

YZ450F_1384

This chapter covers information and servicing procedures for the fuel system components of motorcycles scooters, UTV’s and ATVs.

TROUBLESHOOTING

Engine cranks but won’t start

  • No fuel in tank
  • No fuel to carburetor
  • Cylinder flooded with fuel
  • No spark at plug
  • Clogged air cleaner
  • Intake air leak
  • Improper throttle operation
  • Compression too low
  • Contaminated fuel
  • Faulty auto bystarter
  • Clogged idle system or auto bystarter passages

Engine lacks power

  • Clogged air cleaner
  • Faulty carburetor
  • Faulty ignition system

Lean mixture

  • Clogged carburetor fuel jets
  • Float level too low
  • Faulty float valve
  • Intake air leak
  • Clogged fuel tank cap breather hole
  • Bent, kinked or restricted fuel line

Rich mixture

  • Float level too high
  • Clogged air jets
  • Clogged air cleaner
  • Faulty auto bystarter
  • Faulty float valve

Engine idles roughly, stalls or runs poorly

  • Clogged fuel system
  • Faulty auto bystarter (electric choke)
  • Ignition malfunction
  • Faulty carburetor
  • Poor quality fuel
  • Lean or rich mixture
  • Incorrect idle speed
  • Contaminated fuel
  • Intake air leak
  • Incorrect pilot screw adjustment
  • Float level incorrect

Misfiring during acceleration

  • Faulty ignition system
  • Faulty carburetor
  • Faulty accelerator pump

Backfiring at deceleration

  • Float level too low
  • Incorrectly adjusted carburetor
  • Lean mixture in idle system

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