Checking with a vacuum gauge
Connect a gauge to the intake manifold. Warm up the engine and leave it to idle.
If the engine is good, the meter should read 17-22 inches and the needle should twitch evenly.
If the meter reading is lower than necessary, then the following reasons are likely: the gasket between the intake manifold and the carburetor or throttle is leaking, the vacuum hose is leaking, the ignition timing or camshaft angle is not adjusted.
If the meter reading is 8 inches below normal, the intake manifold gasket is leaking or the injector is faulty.
If the arrow at regular intervals falls 2 inches below the normal mark, the valves are leaking.
If the arrow jerks strongly unevenly down, the valve is sticking or the spark plugs are faulty.
Four-inch needle vibration and exhaust fumes - worn valve guides.
Rapid vibration as engine speed increases - intake manifold or head gasket is leaking, valve springs are worn out, valves are burnt, or spark plugs are faulty.
Weak twitching of the arrow near the normal 1 inch mark - ignition problems.
Strong twitching of the arrow - the cylinder head gasket is damaged.
If the arrow slowly deviates for large segments, the fuel is not mixed correctly, the intake manifold or throttle gasket is leaking.
Raise the RPM to 2500 and shut off the engine, the needle should drop to almost zero, then rise 5 inches above the normal mark and return to the normal mark.
If this does not happen, then the piston rings are worn out.
If there is a long delay, the exhaust system is clogged.
Compression test
1. Shut off the ignition system by disconnecting the ignition high voltage wire from the distributor cap and grounding it to the engine block.
2. Connect a compression tester to the spark plug hole of cylinder N1.
3. Fully open the throttle and turn the engine over with the starter. After one or two revolutions, the compression pressure should rise to the maximum mark and then stabilize. Write down the result.
4. Carry out a similar test with the remaining cylinders and record the readings.
5. The pressure in all cylinders must be the same. A difference of more than 2 bar between any two cylinders indicates a malfunction. In a healthy engine, pressure should build up quickly. Low pressure on the first stroke, gradually increasing on subsequent strokes, indicates that the piston rings are worn. Low first stroke pressure that does not build up on subsequent strokes indicates a valve leak or blown head gasket. Deposits on the bottom of the valves can also cause low compression.
6. If you have any doubts during the inspection, contact experienced specialists.
7. If the pressure in any cylinder is too low, carry out the following test to determine the cause. Pour a teaspoon of clean engine oil into the cylinder through the spark plug hole and repeat the pressure test.
8. If after adding oil the compression pressure has increased, then this means that the piston or cylinder is worn. If the pressure does not increase, then the cause is worn or burned valves or a blown cylinder head gasket.
9. Low pressure in two adjacent cylinders almost always means that a head gasket is blown between them.
10. If the pressure in one of the cylinders is approximately 20% lower than in the others and the engine does not idle well, this means that the cause may be a worn camshaft cam.
11. If the pressure is too high, then most likely the walls of the combustion chambers are covered with coal deposits.
12. After completing the check, screw the spark plugs into place and connect the ignition system.