ENGINE RUNS BUT LACKS POWER - TM-5-4320-234-120040

TM 5-4320-234-12

MALFUNCTION

TEST OR INSPECTION

CORRECTIVE ACTION

ENGINE--Continued

e. Install the thermostat, water outlet elbow and gasket on the engine. Secure the water outlet elbow with nuts

and lockwashers.

f. Connect the water pump bypass tube and radiator top hose. Service the engine coolant system.

Start the engine and run it until it reaches operating temperature, and check for leaks.

Correct any leaks noted.

Step 8. Check for incorrect ignition timing.

a. Start the engine and idle at 600 rpm.

b. Use a timing light, connected to the rear spark plug and check that the IGN-M indication on the flywheel is

aligned with the timing pointer. If it is not aligned, loosen the magneto mounting hardware and rotate the

magneto slightly until the IGN-M indication on the flywheel is obtained.

6. ENGINE RUNS BUT LACKS POWER

Step 1. Check that throttle control is in full speed position.

a. If throttle control is not in full speed position push in throttle control to provide full speed operation. Adjust

throttle control if necessary.

b. To adjust the throttle control rod, loosen nut at ball joint and adjust throttle rod length until operating range

of 2750 rpm is obtained. Tighten throttle rod ball joint locknut.

Step 2. Check for restriction in air cleaner.

a. Loosen the wing bolt on the clamp assembly and remove the dust cover.

b. Remove wing nut and remove the element.

CAUTION

Do not use gasoline or other solvents for cleaning the air cleaner element.

c. To clean the element, use a 1/8 inch air nozzle with 100 psi maximum compressed air, blowing from the

inside toward the outside until all dust is removed.

d. An alternate method of cleaning the element is to wash it with a nonsudsing detergent in a container large

enough to immerse the element. Allow it to soak for 10 minutes minimum and agitate it for 2 minutes to

dislodge all dirt. Rinse with clean water, using water pressure from a tap with pressure of less than 40 psi. Air

dry thoroughly before reinstallation.

e. Insert a light bulb in the cleaned element and carefully check for holes, cracks, or ruptures. Any hole in the

element will necessitate element replacement.

f. Install element and secure with wing nut. Install dust cover and tighten clamp assembly wing bolt.

Step 3. Check for stuck weather cap on muffler.

Free weather cap, squirting oil on swivel and tapping lightly with a hammer.

Step 4. Check for incorrect ignition timing.

a. Start the engine and idle at 600 rpm.

b. Using a timing light, connected to the rear spark plug and check that the IGN-M indication on the flywheel is

aligned with the timing pointer. If it is not aligned, loosen the magneto mounting hardware and rotate the

magneto slightly until the IGN-M indication on the flywheel is obtained.

7. ENGINE BACKFIRES

Step 1. Check for incorrect ignition timing.

a. Start the engine and idle at 600 rpm.

b. Use a timing light, connected to the rear spark plug and check that the IGN-M indication on the flywheel is

aligned with the timing pointer. If it is not aligned, loosen the magneto mounting hardware and rotate the

magneto slightly until the IGN-M indication on the flywheel is obtained.

8. ENGINE OPERATED ERRATICALLY

Step 1. Check for improper fuel mixture.

a. Turn the carburetor main adjusting screw clockwise to reduce the fuel to the engine until the engine begins

to miss due to a lean fuel mixture.

b. Turn the adjusting screw counterclockwise until the engine runs smoothly without missing.

c. With the engine at idle, turn the carburetor idle mixture adjustment screw clockwise to cut off air. making the

fuel mixture richer, until the engine starts to run roughly due to excessively rich mixture.

d. Turn the idle mixture adjustment screw counterclockwise to obtain the smoothest idle operation possible.

Step 2. Check for defective spark plugs.

a. Tag and disconnect the shielded spark plug cables from the spark plugs. Using a spark plug wrench,

remove the spark plugs.

WARNING

Dry cleaning solvent PD-680, used to clean parts is potentially dangerous to

personnel and property. Avoid repeated and prolonged skin contact. Do not use

near open flame or excessive heat. Flash point of solvent is 100 F.-138 F. (38 C.-

59 C).

b. Wipe the exterior of the spark plugs with a cloth dampened with dry cleaning solvent (Fed Spec. PD-680),

dry thoroughly.

c. Check the ceramic insulator for cracks, porosity, and other damage.

d. If the electrodes of spark plugs are not too badly burned, remove the scale and other deposits from them.

This can be done by a sand-blast type cleaner or with a contact file.

e. Inspect the electrodes for severe burning cracks, and other damage. Replace any spark plug whose

condition is doubtful.

f. Make sure all spark plugs are gapped to 0.025 inch before installation. Install and torque the spark plugs to

35 foot pounds.

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