Carburetor question '78 mercury 800 (80hp)

I bought my very first boat a month ago and took it out for the first time 2 weeks ago. The boat never had any problems starting up on a garden hose in my driveway, but it did have a problem going into gear on the lake. Every time I put the boat into gear it would die. I put the idling throttle up a bit and was able to get it into gear. After idling a round a bit I killed the engine and we sat around for about 20mins to fish. Could not get the engine started again for another 30mins of cranking but did eventually get it started. After running at WOT for a bit the boat didnt seem to have any problems starting up or going into gear. This is all just backstory for my real question.

So after this experience I decided it would be best to decarb the engine. I put seafoam into a spray bottle and sprayed it in the carbs. As far as I can tell I think there is only 2 carbs on this 4 cylinder engine. When i sprayed the seafoam into the top carb nothing seamed to happen but when i sprayed it into the bottom carb, the engine would smoke up and bog down like I expected. The engine doesn't seem to be running very rough but am I only running on one carb? I'm concerned after seeing not effect on the engine after spraying seafoam into the top carb.

Re: Carburetor question '78 mercury 800 (80hp)

check the spark on the top cylinders 1 may not be firing. Carb adjustments may have to be made but check the plugs plug wires to be sure there all inserted in the coils and to the plugs tightly etc. Check the plug condition as well pictures are always a good idea. Plugs brown? plugs black? plugs white?Oily? Dry? All about the same?

Re: Carburetor question '78 mercury 800 (80hp)

They like to be started with as much gas as you can "force" into it. When the primer bulb feels hard give it a few more pumps.Choke her and get the idle control arm up a bit as well. Is your primer bulb holding or is it bleeding down ? Sounds like the idle circuit on the upper carb is blocked,can you change the idle rpms with the idle/slow speed jet on that carb.Sometimes by adjusting that screw the blockage comes loose. In reality it sounds like the entire fuel system needs to be gone over.