Vacuum meter
Typical Vacuum Gauge Readings
1. Low constant pressure
2. Low changing pressure
3. Regular pressure surges
4. Random pressure surges
5. Fast arrow vibration
6. Strong fluctuations in pressure
7. Constant pressure drop
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.