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Compression Test
IF THE IMAGE IS TOO SMALL, click it.

1. Ensure oil in crankcase is of the correct viscosity and at proper level and battery is properly charged. Operate vehicle until engine is at normal operating temperature. Turn ignition switch to the OFF position, then remove all spark plugs.

2. Set throttle plate in wide-open position.

3. Install a compression gauge such as Rotunda Compression Tester 059-00009 or equivalent in No. 1 cylinder.

4. Install an auxiliary starter switch in starting circuit. With ignition switch in the OFF position, and using auxiliary starter switch, crank engine at least five compression strokes and record highest reading. Note the approximate number of compression strokes required to obtain the highest reading.

5. Repeat test on each cylinder cranking the engine approximately the same number of compression strokes.

Test Conclusion:
The indicated compression pressures are considered within specification if the lowest reading cylinder is above 75 percent of the highest. Refer to the Compression Pressure Limit Chart.

If one or more cylinders read low, squirt approximately one tablespoon of XO-20W50-QR (ESR-M2C179-A) or equivalent engine oil on top of the pistons in the low reading cylinders. Repeat compression pressure check on these cylinders.

1. If compression improves considerably, piston rings are at fault.

2. If compression does not improve, valves are sticking or seating poorly.

3. If two adjacent cylinders indicate low compression pressures and squirting oil on pistons does not increase compression, cause may be a cylinder head gasket leak between cylinders. Engine oil and/or coolant in cylinders could result from this problem.

It is recommended the Compression Pressure Limit Chart be used when checking cylinder compression so that the lowest reading number is at least 75 percent of the highest reading.
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See also: Dissolved Gas Test Kit
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See this page for vacuum gauge instructions. I recommend something like this:

-Clickit

If compression is too HIGH, it's probably due to deposits in the combustion chambers. Removing them is cheap & easy.

With the engine FULLY warmed-up to operating temp, and at high rev (~1500-2500RPM), drip or spray clean (distilled is best) water into the throttle. That's pretty much it. You want to get JUST enough water going in to make the engine cough, but NOT anywhere close to enough to hydraulic a piston. That's why the RPM has to be far above idle - so there's enough airflow to keep a puddle from forming anywhere, and then suddenly splashing into a chamber.

Just like when a head gasket leaks & allows coolant into a cylinder, the water starts to evaporate when it hits the hot metal. But when the piston compresses it, it liquefies again and is forced into the pores of any carbon deposits. When the cylinder fires, the water explodes into steam, blasting the carbon off. If there WAS any in your engine, you should see the exhaust turn dark initially, and then get whiter as you run out of carbon in the engine.