Mercury 100 FourStroke, Service Manual

Page: 184 / 574

3B-22 - FUEL SYSTEM 90-830234R3 DECEMBER 1997
Problem: Engine Runs Too Lean
Possible Cause Corrective Action
Carburetor is loose. Air leaks past mixing chamber
cover. Tighten bolts securely. Tighten cover or replace gas-
ket.
Fuel level is too low. Reset float level.
Clogged high speed jet. Inspect jet for varnish or debris and clean.
Restricted fuel flow to carburetor. Check fuel lines and filter(s) for restricted flow.
Incorrect high speed jet. Refer to main jet chart and replace with proper jet.
Idle mixture set too lean. Adjust to run richer (turn idle mix screw counter-
clockwise).
Air leakage into fuel system. Inspect fuel line connections, hose clamps, fuel
pump and fuel outlet tube (located in fuel tank) for
loose fittings.
Anti-siphon valve restricting fuel flow. Refer to Section 3A for checking for restriction of
fuel flow caused by anti-siphon valve.
Problems:
-Engine Idles Rough And Stalls
-Engine Runs Uneven Or Surges
-Engine Will Not Accelerate
Possible Cause Corrective Action
Fuel tank air vent closed or restricted. Air vent must be open all the way and free from re-
strictions.
A pinched, cut or restricted fuel line; also loose fuel
line connection. Check all fuel lines and replace as needed. Check
and tighten all fuel line connections.
A dirty or restricted fuel filter. Check, replace, or clean all fuel filters.
Restricted filter in fuel tank. Clean by rinsing in clean lead-free gasoline or kero-
sene.
Improperly mixed fuel; contaminants (water, dirt,
etc,) in fuel. Check fuel and replace,
if necessary.
An inlet needle (in carburetor) that is either stuck
open or closed. (A needle, that is stuck open, will
cause a flooding condition. A needle, that is stuck
closed, will prevent fuel from entering carburetor.) Remove and replace with new inlet needle.
Incorrect idle mixture adjustment. Re-adjust.
Carburetor is loose. Tighten bolts securely.
Chamber cover leaking air. Tighten or replace gasket.
Off idle holes plugged. Blow out with compressed air.
Main nozzle or idle nozzle air bleed holes plugged. Blow out with compressed air.
Improper main jet or restricted jet. Clean or replace with proper jet (refer to “Main Jet
Chart”).
Damaged reed(s). Inspect reeds as outlined in Section 4A.
A crack in the fuel pick-up outlet tube (located in fuel
tank). Replace.