Aloha, I have twin 45 hp Hondas. One of the engines runs only on one cylinder when it is in idle. When I throttle it up it seems to run on three. I notice a lot of unburned gas, the black gooey thing when I come in. Mechanics checked the ignition part sparkplugs,wires,and coils and found it to be okay. When he checked the carburetors he noticed that when he put his hand over the top two carbs the engine runs smoother. He says that there is probably a vacuum leak but couldn't find it. Did anybody run into a situation like this? Any suggestions? Thank You