I have a 92 Mercury 40 hp 4cyl. on my whaler. I just purchased the boat and took it out for a shakedown. The motor runs really well except for the random backfire and stall. I had changed the fuel thinking it may be bad with no change. I also changed all the spark plugs figuring I would start with the cheap and easy first. The spark plugs seemed to help some but it will still backfire and die going from reverse to neutral to forward and other way. It is oil injected and the old plugs seemed like they may be a little heavy with oil. Can anyone give me an idea of where to go next. Could it be running too much oil? It seems like it starts to bog down when idling around.
