My 1996 60 mercury dies in the rpm range of 3000 to 4000. If I'm running along wide open and throttle back it will stall in that range, but run okay at lower/higher RPMs. It runs fine below or above that range. It normally does this after running for a while and when I open the cowling it is wet inside - but not flooded out. The motor is mounted on a 22' pontoon boat. I think it has something to do with the inside getting wet during operation. Any ideas?
Sounds very possible that the wetness may have something to do with it. I would get a timing light and test all of the cylinders to see if they are firing when it acts up. If they are all firing when it acts up it could be your water issue or maybe even a fuel issue. Try spraying starting fluid directly into the carburetors when it is acting up and see if it all the sudden takes off when you spray in there. If it does then you have a fuel problem. It's also always a good idea to take off the fuel filter and see if it is stopped up. You can blow through it backwards...it should be as easy as blowing through a straw. Also see if there is any water that is in the fuel filter. If so then that means there is most likely water mixed in with the fuel in the carburetors. Get the water out if so.
I'm still at a loss. I pulled the drain plugs out of the carbs to check for water - none. It still dies in the mid-range, but runs okay at slow or high speeds. When I first head out it runs okay at all ranges and has the problem after an hour or so of running. Plugs look good and cylinders don't look like water is "steam cleaning" them. It hasn't left me stranded, but it makes for some tense boating. Any other ideas?
I have the same problem now with my 60 hp Mercury Bigfoot. It is mounted on a 24 ft pontoon, I havd a problem last year with it dropping rpms after I was out for about 45 mins or so, there was water getting in, finally figured out it was coming in around the seal to the cover. I replaced the seal and it ran great for the rest of last year and the beginning of this year until just recently it is doing the exact same thing as your bigfoot. If you full throttle or slow it is fine but if you throttle back to mid speed it sputters and dies. I am going to try the seafoam product but if you know of anything else I would be most appreciative.
Let me know how the seafoam works out. I have raised my motor two bolt holes higher on the transom of my pontoon boat. That seems to have lessened the problem, but when I get weeds around the motor it still gets wet and causes the problem. Look at your cavation plate in relation to the bottom of the boat. It should be about even or slightly (1") lower than the bottom of the boat. Seems like Mercury has a problem with the 60 hp Bigfoot but doesn't do anything about it.
I will look at it today, I spent alot of money for a mechanic who did not even suggest the water coming up around the cover seal. How did you lift this motor? I also put hydra foils on the lower unit as well to help with the spray. My boat is kept in the water until November. I am getting close to pulling the motor and replacing with a Yamaha or Honda...It seems like there is just one problem after another. If you look behind a pontoon boat underway it looks like a big giant fountain spraying everywhere. Incidentally, I have a Merc 25 hp 2 stroke on my jon boat and it runs like a top. You can definately feel the difference when you close the engine cover on the 25 hp. My email is whcsullivan@msn.com I will keep you posted.
1996 60hp mercury stalling at mid speed
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