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COMPRESSION PRESSURE
The compression of a cylinder is a good indicator of its
internal condition.
The decision to overhaul the cylinder is often based on
the results of a compression test. Periodic maintenance
records kept at your dealership should include compres-
sion reading for each maintenance service.
Compression pressure
Standard
Service limit
Low compression pressure can indicate any of the fol-
lowing conditions :
● Excessively worn cylinder wall
● Worn-down piston or piston rings
● Piston rings stuck in grooves
● Poor seating of valves
● Ruptured or otherwise defective cylinder head gasket
◉ COMPRESSION TEST PROCEDURE
NOTE:
� Before testing the engine for compression pres-
sure, make sure that the cylinder head bolts are
tightened to the specified torque values and
valves are properly adjusted.
� Have the engine warmed up by idling before testing.
� Be sure that the battery used is in fully-charged
condition.
Remove the parts concerned and test the compression
pressure in the following manner.
● Loosen the oil cooler mounting bolts from the frame.
● Remove all the spark plug.
● Fit the compression gauge in one of the plug holes,
while taking care that the connection is tight.
● Keep the throttle grip in full-open position.
● Crank the engine a few seconds with the starter, and
record the maximum gauge reading as the compres-
sion of that cylinder.
Compression gauge : 09915 - 64510
2
14~16 kg/cm
(at 600 rpm)
2
12 kg/cm
(at 600 rpm)
PERIODIC MAINTENANCE 2-20
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Questions and answers
I have a 2002 gv250. It's getting gas via fuel pump to the carbs and there's good spark, seems to have good compression but it still won't start. The starter seems to work fine. Anything else I should check? It appears to have no fuel pressure regulator either.
If a 2002 HYOSUNG Aquila 250 (GV250) has fuel, spark, and compression but still won't start, check the following:
1. Clogged Jets in Carburetor – Clean the carburetor jets to ensure proper fuel delivery.
2. Float-Chamber Fuel Level – Adjust the fuel level in the carburetor if necessary.
3. Fouled Spark Plug – Clean or replace the spark plug.
4. Incorrect Spark Plug Gap – Adjust or replace the spark plug if the gap is incorrect.
5. Clogged Air Cleaner Element – Clean the air filter to allow proper airflow.
6. Defective Air Intake Pipe – Retighten or replace if necessary.
If the issue persists, consult a qualified service mechanic.
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I have a 2011 gv250. It is a EFI system It's getting gas via fuel pump to the carbs and there's good spark, seems to have good compression but it still won't start. The starter seems to work fine. Anything else I should check? It appears to have no fuel pressure regulator either.
If a 2011 HYOSUNG Aquila 250 (GV250) with an EFI system has fuel, spark, and compression but still won't start, consider the following checks:
1. Fuel Injection System: Ensure the fuel injector is not clogged and is delivering fuel properly.
2. ECU (Electronic Control Unit): Check for any fault codes that may indicate an issue with sensors or fuel mapping.
3. Ignition Timing: Verify that the ignition timing is correct and the CDI unit is functioning properly.
4. Air Intake System: Inspect the air filter and intake system for blockages.
5. Battery and Electrical Connections: Ensure the battery is fully charged and that all electrical connections, including grounds, are secure.
6. Throttle Position Sensor: Check if the throttle position sensor is functioning correctly.
7. Fuel Pump and Pressure: Confirm that the fuel pump is working and providing adequate pressure.
If these checks do not resolve the issue, consult a Hyosung dealer or qualified mechanic.
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