Vacuum Gauge Reading
A cheap, easy way to get a little insight to the internal condition of the engine. Here is a combination fuel and vacuum gauge http://amzn.to/2pQkFL6 Here is the user manual for above combination fuel and vacuum gauge https://actron.com/sites/default/files/pdf_english_16176.pdf Always take into account your elevation when dealing with vacuum and pressure. Unfortunately the new version of google sites doesn't seem to like animated images at all.
Link to the animated images. https://photos.app.goo.gl/3PPDmCDw3k9byyDP8
NORMAL ENGINE: Steady reading of 17-21 when engine is idling.
NORMAL ENGINE: When throttle is opened and closed rapidly needle falls to 2 and swings back to 24 or 25, falling back to normal idle reading Indicates rings and valves OK
POOR RINGS: Engine idling, hand reading steadily, but 2-4 points lower than normal. This may also indicate poor or contaminated engine oil, late ignition timing, a leaky vacuum hose and a leaking gasket between the intake and carb or throttle body.
POOR RINGS/POOR OIL: When throttle is opened and closed rapidly needle falls to 0 and rises to only 24 or less.
STICKING VALVE: Needle drops occasionally about 4 points at idle speed. May also be caused by ignition misfire. Read the spark plugs.
BURNT VALVE: Needle drops regularly by several points at idle speed.
LEAKY VALVE: Needle drops 2-4 points when valve should close. short circuiting individual spark plugs will indicate cylinder in which the valve is defective, when engine idling.
WORN VALVE GUIDES: Rapid fluctuation of needle between 17 and 21, when engine idling. Exhaust smoke may also be present. If engine speed goes up with fluctuation, check for a leaking intake manifold gasket, head gasket, weak valve springs, burned valves, or ignition misfire.
WEAK VALVE SPRINGS: engine running fast, the needle moves between 10 and 21.Further increase in engine speed increases needle variations.
LATE VALVE TIMING: with engine running at a higher idle speed needle reads from 8 to 15 and remains steady.
RETARDED IGNITION: needle gives steady reading between 17 and 19 with engine running at a higher idle speed.
DEFECTIVE IGNITION: if needle moves slowly between 14 and 16 at normal idle, check ignition components (plug gaps closed up/fouled,contacts not synchronized).
INTAKE SYSTEM LEAK: with engine running at idle or fast idle speeds needle reads between 3 and 5. Check induction manifold gaskets.
HEAD GASKET LEAK: (leaking between cylinders): needle moves backwards and forwards regularly between 5 and 17.
EXHAUST SYSTEM BLOCKAGE: high reading when engine first started, falling back to 1 or zero and gradually increasing to 15 or 17.
INCORRECT FUEL ADJUSTMENT: needle moves slowly backwards and forwards between 18 and 21.Check engine idle mixture.