'99 Johnson 115 stumbles, drops cylinder?

[Captain Jeff]

Hello...my 1999 Johnson OceanPro 115 on an 18' Angler center console runs great until around 3500 RPM. Beyond this it intermittently/ randomly "stumbles". It shakes a little and seems to lose power maybe for a second, then again a couple seconds later, etc. It reminds me of when I changed plugs in my car and one of the wire boots had a pinhole in it. The wire would arc and drop that cylinder at higher RPM. It also will happen on the Johnson at lower RPM when you try to accelerate quickly.<br /><br />The motor is well maintained. All four carbs rebuilt last year, new VRO. Compression last year was perfect. Fresh, regular gas. Champion QL78YC plugs. I thought the prop hub might be slipping but it seems in great shape. The boat was used over the winter in FL as well and has only been unused for about a month. The only things I did since then were change the lower unit oil, inspect the engine, lube linkages etc, clean on engine fuel filter and.....install an inline screw on oil filter type water separating fuel filter. Yes I attached a piece of clear line between the primer and engine and there are some (very few) air bubbles of unknown origin. However, when the engine is stumbling there are no air bubbles present anywhere visible. I also ran it at night and saw no spark plug wire arcing.<br /><br />Please help, I've tried everything I can think of, you guys are the experts!