Fuel System; Fuel System Troubleshooting - Mercury 15XD Service Manual

Fuel System Troubleshooting

General Information
Problems that are thought to be caused by the fuel system may, in reality, be something
completely different. Items, that are shown in the list on the right, could give the impres-
sion that there is a problem in the fuel system
1. Propeller
2. Spark Plugs
3. Ignition Timing
4. Ignition Spark Voltage
5. Cylinder Compression
6. Reed Valves
Typical symptoms and solutions in troubleshooting a fuel system are shown below:
Problem: Engine Turns Over but Will Not Start or Starts Hard When Cold
Problem: Engine Idles Rough and Stalls.
Problem: Engine Runs Uneven or Surges.
Problem: Engine Will Not Accelerate.
Possible Cause
Improper starting procedure used.
Fuel tank empty or too low. Improperly mixed fuel.
Contaminants (water,dirt, etc.) in fuel.
Fuel tank air vent closed or restricted.
Pinched, cut, restricted fuel line or loose fuel line
connection.
Dirty or restricted fuel filter.
Choke solenoid or enrichment valve not operating. Inspect solenoid or valve and wiring. Replace as
Needle and seat in carburetor that is either stuck
open (flooding) or closed (no fuel).
Improper carburetor jet, restricted jet or idle mix-
ture screw out of adjustment.
Improper float level.
Low fuel pump pressure.
Defective anti-siphon valve.
90-826883R2 JUNE 1998
.
Corrective Action
Review starting procedure as outlined in "Opera-
tion and Maintenance Manual."
Check fuel in tank and replace or add whichever is
necessary.
Check air vent on fuel tank. Air vent must be open
all-the-way and free from any contaminants.
Inspect all fuel lines and replace as needed. Tight-
en fuel line connections.
Inspect and replace or clean all fuel filters.
required.
Refer to carburetor disassembly in this section.
Refer to carburetor adjustments in this section.
Refer to carburetor adjustments in this section.
Disassemble and inspect fuel pump components.
Inspect valve and/or test engine without valve in

fuel system.

CARBURETOR/FUEL PUMP
Page 3A-15