I theorize stuck valves on these older motors may be because of the ethanol in the fuel. If it is a stuck valve, you can usually fix that right on the vehicle by first identifying which cylinder is the culprit, and then pulling that sparkplug. With a small punch you can gently tap the valve back in place, then crank the engine over and repeat until the valve moves freely again.
To identify which cylinder has the stuck valve, you can start at the exhaust pipe and with the engine running, and your hand in the exhaust stream, feel for the side that has a miss. That will narrow it down to one side. Now for the shocking part. With the engine running, you need to pull the wires one at a time and see if there is a loss of RPM, or an added roughness to the idle. If the plug is pulled and there is no change, then you have found the bad cylinder. This was often referred to as a poor mans compression test. Replace the wire and move on to the next cylinder.
These jobs are much easier with a second person.
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