help with 97 merc 50hp

[kerryd15]

took my new used boat out today.Ran it at home with the muffs and seemed to run well. when i got to the lake it started good and idled, let it warm up a bit then went to half throttle for a minute or so. tried to open it up and it started to pulsate like one piston not firing. so i turned around to troll back with the electric- battery dead. The engine started back up but i could only idle back to shore. At home i pulled the plugs and the bottom one was wet. still had good spark on all three plugs. i pulled the idle air screws and prayed carb cleaner in them, same with the vent beside the idle screw. I pulled the bowl plug and cleaned the jet there with cleaner and air, as well as the jet in the front of the carb. What ports am i missing? I didn't want to take the carbs off because i didn't have a kit and i wasn't sure if i would screw up the syncronization of the carbs. Any thing else i should check. i had fresh gas, stabilizer, a little sea foam, and a brand new gas tank. could it be the accelerator pump?

Another thing I question is when i went down the road I had the motor raised all the way up and it sits past a 45 degree angle could i be flooding it going down the road? There really isn't another position to lock the motor, should i be unhooking the gas line?

[jentz]

Sometimes a plug under the pressure in the cylinder will not spark.I'd start by replacing just that plug.

[walleyemaniac]

I had a coil go bad once, had what I thought was good spark when looking at the plug, but it wasn't good enough at higher rpm's. Mechanic told me to replace the coil, worked fine. Only reason I say this is wet plug makes me think its not firing.

Otherwise I would say maybe the impeller in the water pump. When you had it hooked up to the hose it was forcing water thru it. Out on the lake it had to suck it up. I think most motors have a built in safety if the motor is running to hot they will only open up to half throttle at the most, maybe even only idle. I don't know if something like that would cause a wet plug or not. I don't know if the safety switch might cut out a cylinder to keep the power down cause I know when it happened to my buddy the motor was pretty sluggish.

[Valv]

Wet plug is from unburned fuel. Did you set the idle screws back as they were before, counting the turns ?

Try to swap plugs, and also coils, if the problem persist on another cylinder where you swapped the parts you'll know which one is bad.

I don't think it's a carburetor issue.

Try not to travel with motor all the way lifted up, I would buy a transom saver and use it while traveling instead of the OEM lifting lock.

[hanson]

Sounds like my grandpa's motor that I've been putzing around with, his is a 40hp Merc from about that era.

More than likely the coil pack on that cylinder. His motor is a 4 cylinder, twin carb, tiller. When you pull the hood off the motor, there is a plastic cover on the right side, unscrew that cover and the 4 coils will be lined up from top to bottom towards the back of the motor. Its just a couple screws and you can swap it out. Coils are available all over the internet for $20-30 each.

Valv had a good point, move what you believe to be your bad coil from lets say cylinder 4 to cylinder 2. If the problem moves to the other cylinder, you've diagnosed it.

You can also use some insulated pliers to pop plug wires off while the motor is running. When you pull a wire and the motor doesn't change sound or react, you know that is your problem cylinder.

[raymondk]

Check gas line fittings if they are old replace with merc ones don't get after market ones it sounds like the same thing that i had problems with a few years ago since you said you had spark try this first .