Glad it's the end of the boating season. About a week ago I developed this weird pop in my starboard exhaust that I can't figure out. I suspect it sound like a backfire if the exhaust were more conventional. It occurs about once every 3 seconds. There is no indication from the carb side of a cough when it happens so I believe it is downstream a bit. The only thing I can point to leading up to this was a small shot of "Sea Foam" I had administered. I've used this product before and not had a problem. The pop is there when the engine is cold or hot. It seems to be there from idele up to 2000 rpm and it may be there past that, but I can't hear well enough to say. I have a sneaking suspicion it is at cylinder #8 as that exhaust temperature is 30 degrees less that all the others. My first concern was plug wires, so I replaced all of them. No change. Then I suspected a sticky valve. I did a check of all the valves (using the Paul Pletcher running style) and it seems to be right on spec there. I did not have have a set of spark plugs with me but switched cylinder 8 with cylinder 5. No change. By the way I was careful in routing the #7 and #8 wires separately, although I am suspisious of the steel loom it runs through. Can anyone offer a suggestion on where to look next? Other than that it seems to run strong.