225 V6 misfiring, possible valve problems?
Hello everyone! My name is Tony and this is my first post. First off, I have a '69 CJ5 (named Wilford) with the 225 oddfire V6. i bought this guy back in august, and during the initial inspection before purchase i could hear a puffing sound coming through the exhaust. it was frequent, but non-consistent. i was concerned, so i drove it. the motor ran incredibly strong and idled smoothly despite the sound. i figured the thing is 40 years old with the original engine, and it's not going to be perfect. i got a good deal anyways.
okay, so last month i was on my way to work, cruising along at 65 on the freeway, then all the sudden my engine got weak. well ... not really all the sudden, it was a steady, noticeable decrease in power over the course of about 5 seconds or so... to compensate i gave it some more foot, and it started misfiring like crazy. i backed off a bit, and it smoothed out except for an occasional misfire (out of the ordinary for this engine, it never misfires at speed), with only enough throttle input to maintain speed at 50-60 mph. i got to work, pull into my parking space, and rev the engine a few times. normally, this motor purrs, i mean it's really smooth all the time. now it sounds off, and it's shaking a little bit.
i threw the hood up and check the manifolds, and it seemed like everything was firing. i babied it back from work, then on the way back to work the next day, the same thing was happening except i could only go about 45 before the misfires started. i took surface streets back to my apartment, shut it off, and haven't touched it since fearing some kind of internal mechanical failure and not wanting to make it worse.
when i hook up a vacuum gauge, it vibrates between about 15 and 22 inches or so. i haven't done a compression check on all the cylinders (mostly because my compression tester is extremely frustrating to work with because it threads in, but the threaded part doesn't rotate freely on the hose).
literally everything in the ignition system is brand-new except for the distributor base. points, cap, rotor, plugs, wires, coil, and ballast resistor.
any theories or thoughts?