Chug, and not the fun kind...
 

Ok...Working on the Rogue project...454, Bravo 1. There is a major chug when idling, and also at increased rpms...I do NOT think it's the engine. The motor sounds good, and I can idle it right down, and don't hear a miss. However, when this "chug" happens, and it's not timed like a missing cylinder, it's severe enough to shake the engine. Watching the gauges, and they move when it chugs, but I think it's from the shaking. There's also a faint metallic sound, like something rattling around, but it's not like an engine rattle. Once again, I don't think it's an engine miss...Standing behind the boat with the exhaust coming thru hull, it sounds like it's not missing a beat...You can hear the chug the along with a good idle. This happened without the drive on it as well. The gimbal bearing felt smooth and tight before I put the drive on. It will shift into fwd and reverse easily, with no change in the chug. Same with moving the drive up and down...Thanks...Den

Ok...Thinking it may be a miss after all...Coil contacts were corroded. Also, my alternator seems to lose charge when I tach it up a bit, then gets better again when I idle it down...Still looking to be a bit on the low side...Should have about 13 on the meter right? Thanks...Den

You should have more than 13 volts by 2000 rpm, and really should hold voltage at idle (if no stereo or other large loads). 13.6-14.4 is best. Make sure to check with a handheld voltmeter - guages can be off nearly a volt IME.

The up/down in voltage you desrcibe is often a symptom of alternator brushes being worn.