Mercury 25hp 4s dies at WOT after trolling

Hopefully someone can provide some input as I don't want to just start replacing parts for no reason.

I recently installed a 2000 merc 25hp bigfoot on my tracker grizzly.

motor starts up and idles better than any motor I've ever owned, runs awesome (as much as I've run it so far, I rarely have to go far for my fishing spots.)
Into and out of gear, back to neutral, motor runs fine, no sputtering, coughing, sneezing, NADA.

I have been out trolling for the past couple weeks and after trolling for a couple hours and go to WOT the motor will eventually hiccup and then die. I am unable to restart it and it seems as if the motor is flooded at that point.

When I purchased the boat, I didn't realize that it had 24 gallons of gas in it which at the most is a year old. I added ethanol treatment as I know its going to be a PIA to empty out the 24 gallons if it is indeed bad gas.

I am headed out again tonight and will be running an external fuel tank to see if I have the same problem, if I do, then obv its the gas and I'm hoping that a fuel water seperating filter will do the trick so as not to waste over a hundred gallons of gas.

my other thought was that the carb may be gunked up, but I am under the assumption that if that was the case, it would run like crap or not at all when trolling for hours at 1.5mph.

Any help is greatly appreciated.

E

Re: Mercury 25hp 4s dies at WOT after trolling

So I took the boat out trolling again tonight for walleye. I used an external gas tank with fresh fuel, and the boat performed normally. Perfect starting, idling, trolled smooth as silk for at least 2 hours. I switched over to the electric motor just for the quietness and when I was done fishing, started up the big motor. This time it let me run wot for about 10 minutes, (much better than the last 2 trips) and I eventually shut it off, it did not shut off on its own. I trolled around again for another 45 minutes and opened it up wot on the way into the launch, allthough it didn't die on its own, it DEF felt like it was going to until I throttled down to 1/4 throttle. It still felt like it was going to stall out but didn't.

So I've eliminated the full inboard gas tank as having bad fuel, as well as any other internal parts (because the problem still occurred with the external gas tank and fresh fuel)

My adventure tomorrow will be taking off the carb and cleaning it out, as well as installing the fuel/water seperator.

Re: Mercury 25hp 4s dies at WOT after trolling

So the problem was still happening after seafoaming a fresh tank of gas in the external tank. I went out the other night and couldn't even get the motor to start. It was flooded. This morning I took apart the carb and cleaned it out, and didn't really see a whole lot of junk come out. Put it all back together and it fires right up. The only other thing I can think of is that I have my throttle set too high where the controls connect to the motor. I would assume the idle arm needs to be ALL the way up for WOT but I'm not sure.

Re: Mercury 25hp 4s dies at WOT after trolling

seems to be, cleaning the carb did the trick, thanks for all the help guys...............

Re: Mercury 25hp 4s dies at WOT after trolling

I am having a similar problem. Did you pull the carb complete off the manifold?

Or just have to remove the top plate or drop to the float bowl to clean out the internals.

Did you remove any of the jets to clean them out or just try to clean them while still in the carb?

thanks,
fried okra