Problem: Engine Runs Too Lean; Problems: Engine Idles Rough And Stalls; Engine Runs Uneven Or Surges; Engine Will Not Accelerate - Mercury 40 Service Manual

Problem: Engine Runs Too Lean

Possible Cause
Carburetor is loose. Air leaks past mixing chamber
cover.
Fuel level is too low.
Clogged high speed jet.
Restricted fuel flow to carburetor.
Incorrect high speed jet.
Idle mixture set too lean.
Air leakage into fuel system.
Anti-siphon valve restricting fuel flow.
Problems:
-Engine Idles Rough And Stalls

-Engine Runs Uneven Or Surges

-Engine Will Not Accelerate

Possible Cause
Fuel tank air vent closed or restricted.
A pinched, cut or restricted fuel line; also loose fuel
line connection.
A dirty or restricted fuel filter.
Restricted filter in fuel tank.
Improperly mixed fuel; contaminants (water, dirt,
etc,) in fuel.
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.)
Incorrect idle mixture adjustment.
Carburetor is loose.
Chamber cover leaking air.
Off idle holes plugged.
Main nozzle or idle nozzle air bleed holes plugged.
Improper main jet or restricted jet.
Damaged reed(s).
A crack in the fuel pick-up outlet tube (located in fuel
tank).
90-852572R1 JANUARY 1998
Corrective Action
Tighten bolts securely. Tighten cover or replace gas-
ket.
Reset float level.
Inspect jet for varnish or debris and clean.
Check fuel lines and filter(s) for restricted flow.
Refer to main jet chart and replace with proper jet.
Adjust to run richer (turn idle mix screw counter-
clockwise).
Inspect fuel line connections, hose clamps, fuel
pump and fuel outlet tube (located in fuel tank) for
loose fittings.
Refer to Section 3A for checking for restriction of
fuel flow caused by anti-siphon valve.
Corrective Action
Air vent must be open all the way and free from re-
strictions.
Check all fuel lines and replace as needed. Check
and tighten all fuel line connections.
Check, replace, or clean all fuel filters.
Clean by rinsing in clean lead-free gasoline or kero-
sene.
Check fuel and replace,
if necessary.
Remove and replace with new inlet needle.
Re-adjust.
Tighten bolts securely.
Tighten or replace gasket.
Blow out with compressed air.
Blow out with compressed air.
Clean or replace with proper jet (refer to "Main Jet
Chart").
Inspect reeds as outlined in Section 4A.
Replace.
FUEL SYSTEM - 3B-15