An even quicker 'compression' test that would rule out something amiss with a cylinder - just pull the coil wire and crank it over. The starter should labor over each compression evenly. You can pretty easily tell if there is a weak cylinder or not doing this. "WhirrWhirrWheeWhirrWhirrWhirrWheeWhirr".. means there is a problem. (Apologies for doing sound effects in a post!). Make sure there isn't a tight valve before doing other checks (old Volvos, unleaded gas, receding exhaust valves get tight and leak).

Then of course there was the old '51 Ford F350 my Dad had growing up. Had about a million miles. And never before or since had such a massive engine bay been so sparesly populated by a little skinny straight 6. When you cranked the engine it just spun around with appearing to labor over compressions at all. Once for fun I did a compression test on it and got numbers varying between 27 and 35. I don't know how it ran but it did, it would start up and run and while it wasn't going to win any races (against anything) it would move on down the road with a heavy load in it.
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