Mercury 100 FourStroke, Service Manual

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90-830234R3 DECEMBER 1997 FUEL SYSTEM - 3B-21
Problem: Engine Turns Over But Will Not Start Or Starts Hard When Cold
Possible Cause Corrective Action
Improper starting procedure used. Review starting procedure as outlined in “Operation
and Maintenance Manual”.
Fuel tank empty or too low. Improperly mixed fuel.
Contaminants (water, dirt, etc.) in fuel. Check fuel in tank and replace or add whichever is
necessary.
Fuel tank air vent closed or restricted. Check air vent on fuel tank. Air vent must be open
all the way and free from any contaminants.
Pinched, cut, restricted fuel line or loose fuel line
connection. Inspect all fuel lines and replace as needed. Tighten
fuel line connections.
Dirty or restricted fuel filter. Inspect and replace or clean all fuel filters.
Choke solenoid or enrichment valve not operating. Inspect solenoid or valve and wiring. Replace as re-
quired.
Needle and seat in carburetor that is either stuck
open (flooding) or closed (no fuel). Refer to carburetor disassembly in this section.
Improper carburetor jet, restricted jet or idle mixture
screw out of adjustment. Refer to carburetor adjustments in this section.
Improper float level. Refer to carburetor adjustments in this section.
Low fuel pump pressure. Refer to Section 3A “Fuel Pump”.
Defective anti-siphon valve. Refer to Section 3A “Fuel Pump”.
Needle and seat in carburetor that is either stuck
open or closed. Refer to carburetor adjustments in this section.
Improper float level. Refer to carburetor adjustments in this section.
Carburetor loose on intake manifold. Check tightness of carburetor nuts.
Reed block loose or gasket defective.
Using a pressure oil can, apply 2-cycle oil around
reed block housing/crankcase housing matching
surfaces and carburetor base. If engine RPM
changes, tighten bolts/nuts or replace gaskets as
required.
Improperly routed or restricted bleed hose(s). Refer to bleed hose routing in Section 4A “Power-
head”.
Damaged fuel pump diaphragm. Refer to Section 3A “Fuel Pump”.
Carburetor mixing chamber cover leaking air. Tighten screws or replace gasket.
Off idle holes plugged. Blow with compressed air.
Main nozzle or idle nozzle air bleed holes plugged. Blow with compressed air.
Damaged reeds. Refer to Section 4A “Powerhead” for reed inspec-
tion.
Fuel pick-up outlet tube in fuel tank cracked. Replace.
Problem: Unable to Reduce Engine RPM to Slow Idle
Possible Cause Corrective Action
Chipped or broken reeds on reed block. Replace reeds.