Section 5 Engine Diagnostic Tests
30 Diagnostic Repair Manual
Figure 5-10. Checking Engine Misfire
5. If spark jumps tester gap intermittently, the problem
may be in the ignition magneto.
Results
Refer to flow chart.
Test 21 – Check Spark Plugs
Procedure
See Figure 5-11 and Figure 5-12. Remove spark plugs.
Clean with commercial solvent. Replace spark plugs if
badly fouled, if ceramic is cracked, or if badly worn or
damaged.
IMPORTANT NOTE: Do NOT blast clean spark plugs.
Figure 5-11. Spark Plug Conditions
Figure 5-12. Setting Spark Plug Gap
Results
1. Clean and gap or replace sparks plug as
necessary.
2. Refer to flow chart.
Test 22 – Check Carburetion
Procedure
Before making a carburetion check, be sure fuel supply
tank has fresh, clean gasoline.
Check all shutoff valves are open and fuel flows freely
through fuel line.
Make sure choke operates properly.
If engine will not start, remove and inspect spark plug. If
spark plug is wet, look for the following:
• Overchoking
• Excessively rich fuel mixture
• Water in fuel
• Intake valve stuck open
• Needle/float stuck open
If spark plug is dry, look for the following:
• Leaking carburetor mounting gaskets
• Intake valve stuck closed
• Inoperative fuel pump
• Plugged fuel filter(s)
• Varnished carburetor
If engine starts hard or will not start, look for the following:
• Physical damage to AC generator. Check Rotor for
contact with Stator.
• Starting under load. Make sure all loads are
disconnected or turned off before attempting to
crank and start engine.
• Be sure choke is working properly.
1. Remove fuel line at carburetor and ensure there is
adequate fuel entering the carburetor.
2. Remove float bowl and check for foreign matter in
bottom of carburetor bowl.
3. The float is plastic and can be removed for access
to needle for cleaning.
4. With all of this removed, carburetor cleaner can be
used to clean carburetor before assembly.
5. After cleaning carburetor with approved carburetor
cleaner, blow dry with compressed air and
assemble.
Shelf life of gasoline is 30 days. A fuel stabilizer must be
used to ensure fuel is fresh at all times.
Results
If carburetor is varnished, clean or replace. Refer to flow
chart.