5. FUEL SYSTEM AGILITY 125 TROUBLESHOOTING Engine is hard to start Misfiring during acceleration · No spark at plug ( Section 15) · Faulty ignition system · Compression too low · Lean mixture · No fuel to carburetor · Faulty accelerating pump -Clogged fuel filter Engine idles roughly, stalls or runs poorly -Restricted fuel line · Clogged fuel system -Faulty float valve · Ignition malfunction -Incorrectly adjusted float level · Rich or lean mixture · Engine flooded with fuel · Contaminated fuel -Clogged air cleaner · Intake air leak -Fuel overflowing · Incorrect idle speed · Intake air leak · Incorrectly adjusted pilot screw · Contaminated fuel · Clogged idle system or auto bystarter passages · Faulty auto bystarter · Incorrectly adjusted float level · Clogged idle system or auto bystarter passages Lean mixture Rich mixture · Clogged fuel jets · Faulty auto bystarter · Faulty float valve · Faulty float valve · Float level too low · Float level too high · Clogged fuel system · Clogged air jets · Intake air leak · Dirty air cleaner · Improper vacuum piston operation · Flooded carburetor · Improper throttle operation Backfiring at deceleration · Lean mixture in idle system · Improper air cut-off valve operation 5-3