Mercury 25hp Bigfoot - won't run

[Earl Keese]

I have 2003 Merc 25 Bigfoot - Motor has history of running poorly since new. Very low hours. Believe it to be fuel system. Motor will run then shut down, usually at high rpm. Once shut down will not start again. Can run for 10-30 minutes. Sounds like it is running out of gas but there is plenty. I have replaced lines, filter and gas tank. Mechanic has cleaned and adjusted carb. I have changed plugs, and had a water seperater filter added. This year mechanic replaced the fuel pump as the diaphram was ruptured. It ran great for 30 minutes and now doing all the things it was before. I know gas is ok as I run it in other boats. Extremely frustrated with this motor. Is there any thoughts as to where to check next?

 

[Mr. Florida]

Re: Mercury 25hp Bigfoot - won't run

It could be a sensor or the ECM. Sounds like one of the sensors is telling it to shut down, BUT if that is truly the case you should be able to start it right up after the shutdown. Do any of the audible alarms go off before it shuts down?

 

[Earl Keese]

Re: Mercury 25hp Bigfoot - won't run

Greetings - No there are no alarms that sound.
I recently bipassed the water seperator filter and ran direct to the motor. The motor actually ran great for about an hour. Even had the maraine mechanic with me in the boat. He suggested changing the filter and reconnecting. Which I did. Ran ok for about 5 minutes then ran very erract. Including shutting down and not starting. I tried to bypass again and same problem. Any thoughts.

Thank you

 

[Mr. Florida]

Re: Mercury 25hp Bigfoot - won't run

Could be the fuel pump or carb. In the Merc repair manual it says if the fuel pump is "ticking" that it needs rebuilt. The fuel pump is mounted on the back of the engine on the valve cover. Could your fuel pickup in the tank be sucking up some crap? Check for cracks or air leaks in fuel line from tank to fuel pump.

 

[japayton6]

Re: Mercury 25hp Bigfoot - won't run

Those carbs have a fuel accellerator pump with a screen in it sometime cloggs up. also have a very small jet in middle of carb under rubber plug that loves to clogg up also check primer bulb and hose like to rott from inside out leavin plastic slivers in hose connection.