I have a 2005 25hp Mercury Bigfoot 4-stroke. I have been struggling with it for the last 10 years or so. It's sporadic, but typically once or twice a year it starts acting up. It just started again.
It had been running well for 3 months and I had to switch to a new tank of gas. I took it for a short cruise and had no issues. The next day it started and I was letting it warm up when it died. After that it wouldn't start. Turned over strong but wouldn't fire. I changed both spark plugs and it started but was running rough. I had it trimmed up to work on the plugs, and when I lowered it, it died. I spent some time trying to get it running again. I could get it to start and run with it trimmed up. The higher it was trimmed the better it ran. I could lower it a bit but would have to rev it to keep it running. If I lowered it all the way it would die and not restart. It was dumping some gas in the water while I was doing this. Bottom line, the spark plugs were not the fix, it was the engine being trimmed up.
This isn't the first time I have experienced the issue with it only running when trimmed up. The previous time I suspected it was a bad fuel filter and the angle of the engine was allowing the fuel to flow better. When I changed the filter it seemed to fix it. In hindsight I suspect it wasn't the filter, but messing with the fuel lines somehow made it start working again. Could be wrong.
This absolutely doesn't make any sense to me, but it occured to me that the issue may correspond to when I switch tanks. I have two that are visually identical. On a hunch I put the original tank back on and it got a little better. I still need to trim it to get it started and I have to keep it rev'd to keep it running, but I could lower the trim all the way and it wouldn't kill. Still had some gas in the water. I even took it for a spin around the lake and as long as I stayed on the throttle it ran. But as soon as I dropped it into neutral un-rev'd it would kill.
I've had it in for service on this issue multiple times. Each time they have indicated it was fuel related. Once they said it was an old fuel line and the inside had degraded and gummed up. Another time they said the sun had caused our gas tank to expand and over pressurize.
In the past 2 years I have replaced the starter, fuel pump, carbureter, filter, fuel line (between tank and motor) and spark plugs.
I am at a loss as to what could explain what I am experiencing and how/why the things I try have the result they do. It almost seems like it is getting too much fuel and when it is trimmed up the carburetor is dumping enough fuel for it not to flood but when trimmed down it floods. I don't understand how this could suddenly happen and I don't know how switching the fuel tank could impact this.
Sorry for the long story, but I am hoping someone has had a similiar experience or could speculate on what might be happening?
Thanks!
It had been running well for 3 months and I had to switch to a new tank of gas. I took it for a short cruise and had no issues. The next day it started and I was letting it warm up when it died. After that it wouldn't start. Turned over strong but wouldn't fire. I changed both spark plugs and it started but was running rough. I had it trimmed up to work on the plugs, and when I lowered it, it died. I spent some time trying to get it running again. I could get it to start and run with it trimmed up. The higher it was trimmed the better it ran. I could lower it a bit but would have to rev it to keep it running. If I lowered it all the way it would die and not restart. It was dumping some gas in the water while I was doing this. Bottom line, the spark plugs were not the fix, it was the engine being trimmed up.
This isn't the first time I have experienced the issue with it only running when trimmed up. The previous time I suspected it was a bad fuel filter and the angle of the engine was allowing the fuel to flow better. When I changed the filter it seemed to fix it. In hindsight I suspect it wasn't the filter, but messing with the fuel lines somehow made it start working again. Could be wrong.
This absolutely doesn't make any sense to me, but it occured to me that the issue may correspond to when I switch tanks. I have two that are visually identical. On a hunch I put the original tank back on and it got a little better. I still need to trim it to get it started and I have to keep it rev'd to keep it running, but I could lower the trim all the way and it wouldn't kill. Still had some gas in the water. I even took it for a spin around the lake and as long as I stayed on the throttle it ran. But as soon as I dropped it into neutral un-rev'd it would kill.
I've had it in for service on this issue multiple times. Each time they have indicated it was fuel related. Once they said it was an old fuel line and the inside had degraded and gummed up. Another time they said the sun had caused our gas tank to expand and over pressurize.
In the past 2 years I have replaced the starter, fuel pump, carbureter, filter, fuel line (between tank and motor) and spark plugs.
I am at a loss as to what could explain what I am experiencing and how/why the things I try have the result they do. It almost seems like it is getting too much fuel and when it is trimmed up the carburetor is dumping enough fuel for it not to flood but when trimmed down it floods. I don't understand how this could suddenly happen and I don't know how switching the fuel tank could impact this.
Sorry for the long story, but I am hoping someone has had a similiar experience or could speculate on what might be happening?
Thanks!
