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Hi, I restored a 1968 Nauset earlier this year, which still has the 1997 Mercury 50 hp motor that had been installed by the previous owner. Boat has run great all summer, until yesterday. I ran up to the lake to pull it out before Irene hit, and she was acting kind of funny. Although she started up fast, a lot of "coughing" and white smoke at start. With a fair amount of rain and falling temps, I figured it might be water in the tank (?), one of two on-deck 6 gallon plastic Moellers.

I ran out and filled up the second tank with fresh gas, a few hours later came and swapped it out. I was happy to see it started up fine, no coughing, no smoke. However, when I went to drive it around the lake and over to the ramp, it was acting funny. Engine sounded fine, popped into gear fine, but try as I might I could not get it up on plane. Once it was in gear, I started moving forward but then got virtually no throttle response - I could put the hammer down and virtually nothing happened.

I plan to bring it to the Merc dealer unless there is something I am overlooking here? Not sure if current issue is related to the problem I thought I had of water in the old tank? Any ideas or thoughts would be appreciated. I have learned a lot about my Whaler over the course of my restoration but am no mechanic so appreciate your insight.

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If you hit the choke for a second, did it get better or worse? If better you have a fuel issue, ie blackage.
if worse it is probably something else.
If you have a helper, remove engine covers and also try restricting airflow to one carb at a time and see if it helps. Similar to above but this way you can see if one carb or the other or both are at fault.
Pull the plugs and see if some appear wetter than the others.

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Possible the gas line connectors to the tank or engine might be leaking, I clamped mine directly to the tank and engine and my boat ran fine.

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Water vapor makes white smoke. Oil burns with a blue tint. If you noticed a lot of truely white smoke that does sound like water. There's a good chance the small fuel lines or more likely carbs are gummed up with oil/water emulsion. Check for fuel restrictions first, and if that can be eliminated move on to carb cleaning.

I had a similar issue due to water in the fuel line. A carb cleaning later, and the engine ran great again.

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Thanks for the input. It is all white smoke. I'm going to try cleaning the carbs with some sea foam and see if that has any effect. I'll let you know.

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If you don't plan to disassemble and clean the carbs, i recommend at least draining the bowls. Seafoam probably won't do a whole lot to remove any accumulated water that could be in there.

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alright, now i am really going to expose my ignorance ... what does it mean to drain the bowls?

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When fuel enters a carb from the pump it first fills a small bowl. There is a float inside the bowl connected to a needle valve to regulate the ammount of fuel that flows into the bowl. From the bowl, the carb mixes the fuel with air, and the fuel-air mixture moves on to the crank case. If you remove the cowling, it is the little dish on the bottom of each carb.

When you intake an ammount of water into the engine, there is a tendancy for some of it to collect in the bowls. On the bottom of the bowl, there will be a drain screw. It is a good idea to remove this screw and drain out whatever fuel and possibly water is in there. In the case of my Evinrude 60HP, i needed to first remove the air box (6 screws) to get to the drain screws. I can't say how easily accessible the drain screws are on your Merc, since i'm just not very farmiliar with the internal layout. In any case, it's not a difficult task with a few wrenches and rags. The drain screw is part 25 on the below diagram of a carb from a 1997 merc 50hp.

http://www.boats.net/parts/search/Merc/Mercury/1997/10504127D/CARBURETOR/parts.html#

If seafoam doesn't do the trick, they will probably need to be disassembled and cleaned to clear any gunky obstructions. If everythig isn't flowing at least a little bit, I don't know if the seafoam will dissolve the gunk. There are a lot of tiny passages to get clogged up, and tiny parts in there. If you want to give that a shot I recommend finding a copy of the service manual, working in a very clean space, and taking a lot of pictures as you go. I had never rebuilt a carb before and was kind of nervous about wrecking something. I managed to pull it off just fine, and learned a whole lot about my motor in the process. It was helpful to have a buddy that knew is stuff better than I did with me. In hindsight, it wasn't too hard at all. Just a lot of little parts.

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Wow - that's very thorough, thanks Swamp. I also appreciate the link - I had searched but hadn't been able to find anything like that.

I just noticed you are also in RI - I'm in East Greenwich. Any interest in lending me a hand when I tear this thing apart? Might be good practice ... I'll throw in free beer!

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Just to close the book on this, I wanted to let you all know the root of the problem was not the fuel - it turned out to be a bad spark plug. Mercury dealer figured it out in no time and got me up and running for small $. Big thanks to you all and to CL Marine in Warwick RI for helping me out.

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Doh! And that is why one should never jump to conclusions, but follow a logical troubleshooting process. Do the easy stuff before going right for the harder thing we all think it is. Compression, Spark, Air, Fuel.

Glad you're up and running.