I have a Merc 454 in a 23' Warlock. I started the boat 2 times earlier this Spring and it ran fine after winterization. I went to put it in the water a couple of weeks later and it would not start, not getting any fuel to the carb. I had the carb rebuilt and put it on a couple of weeks ago. Started it once and it ran fine. A couple of weeks later I put it in the water and it started but was running VERY rough, maybe misfiring. I am not sure where to start. Should I do plugs, cap, rotor and coil? Could it be moisture in the fuel (I filled the tank at the end of last season and treated the fuel as directed by a local shop)? Does it sound like a simple carb adjustment or timing?
Thanks for any input.
Matt

It may be as simple as a filter change and a bit more additive in the fuel or the screen before the carb?

Try disconnecting the fuel line to the carb, put the end into a clear container. Crank it over a few times to pump some fuel into the container and see what comes out. If there was water or slime in the tank over the winter and it got sucked into the filter/seperator, it could be clogged and or pumping it into the carb. It will suck whatever is on the bottom of the tank up first. Filter out as much as it can hold then wam it won;t run. Just check the plugs to see if they have a good spark.