Engine Tends To Cut Out At Full Throttle; Excessive Fuel Consumption - VESPA LX 4T USA Workshop Manual

LX 4T USA
Possible Cause
Wrong ignition advance
Incorrect valve sealing or valve adjustment
Starting rpm too low. Starter motor faulty.
Altered fuel characteristics
Carburettor nozzles clogged or dirty
Engine tends to cut-off at full throttle

ENGINE TENDS TO CUT OUT AT FULL THROTTLE

Possible Cause
Maximum jet clogged
Water or condensate in the carburettor tank
Incorrect ignition advance
Air filter blocked or dirty.
Incorrect float level
Fuel supply pipes choked or clogged
Tank breather hole obstructed
Level in tank too low
Engine tends to cut-off at idle
Possible Cause
Air calibrated holes in carburettor blocked
Defective floating valve
Level in tank too high
Automatic choke stays activated
Air filter blocked or dirty.
Wrong idling adjustment
Spark plug defective or faulty
Pressure too low at the end of compression
Incorrect timing
High fuel consumption
Possible Cause
Air filter blocked or dirty.
ENGINE TENDS TO STOP WHEN IDLING

EXCESSIVE FUEL CONSUMPTION

Operation
Check flywheel keying on the crankshaft, replace control unit if
necessary
Inspect the head and/or restore the correct clearance
Check starting motor.
Drain off the fuel no longer up to standard; then, refill
Dismantle, wash with solvent and dry with compressed air
Operation
Remove the carburettor, wash with solvent and dry with com-
pressed air
Remove the tank, wash with solvent and dry with compressed
air or empty the tank through the appropriate bleed screw
Use a stroboscopic light to check ignition advance and the fly-
wheel correct keying
Dismantle the sponge, wash with water and shampoo, then
soak it in a mixture of 50% petrol and 50% of specific oil (Se-
lenia Air Filter Oil), then hand dry without squeezing, allow to
drip dry and then reassemble.
Restore the correct level in the tank (the float must be parallel
to the upper cover contact plane, that is the throttle valve mem-
brane cover)
Restore the adequate fuel supply
Restore the proper tank aeration
Restore the correct level in the tank (the float must be parallel
to the upper cover contact plane, that is the throttle valve mem-
brane cover)
Operation
Dismantle, wash with solvent and dry with compressed air
Check the proper sliding of the float and the functioning of the
valve
Restore the correct level in the tank (the float must be parallel
to the upper cover contact plane, that is the throttle valve mem-
brane cover)
Check that the piston slides freely and that fuel is supplied to
the automatic choke. Renew if necessary
Dismantle the sponge, wash with water and shampoo, then
soak it in a mixture of 50% petrol and 50% of specific oil (Se-
lenia Air Filter Oil), then hand dry without squeezing, allow to
drip dry and then reassemble.
Correctly adjust the engine idling and check the level of the
C.O.
Replace the spark plug with one with the specified degree and
check the plug gap
Check the thermal group seals and replace worn components
Time the system and check the timing system components
Operation
Dismantle the sponge, wash with water and shampoo, then
soak it in a mixture of 50% petrol and 50% of specific oil (Se-
Troubleshooting
TROUBL - 41