DJ_Allatoona
Petty Officer 2nd Class
- Joined
- Feb 24, 2008
- Messages
- 187
Hoping some experienced Mercury guys read this: I'm approaching the end of my rope with my older motor. I've done everything I know how to do or can do with a shop manual. I cannot solve this problem. If you would read this and weigh in with an idea I'd be very grateful.
It's a Mercury 75HP from 1986. Serial number is 0A984714. Cold start is fine. Couple of gas bulb pumps and she fires up and idles nicely. Sits and purrs while I put my truck away, etc. Then, for the first hour, everything is awesome! She jumps out of the hole. Drops down to No Wake speed under bridges without a hiccup. Quick response to all throttle changes. Seriously, I couldn't be happier. Then, after I've stopped for the first time, to fish or swim or play with the kids, that's when "The Problem" begins.
Here's what I call "The Problem". After this motor has been running awhile, like I said, 45 minutes or an hour, restarting it is difficult. I have to pump the crap out of the fuel bulb, and crank it for some time before it starts. Much harder start than when it's cold. Idling is very low and rough, and I have to play with the idle throttle to keep it from stalling. During "The Problem", the motor dies when I push the throttle forward. Like, it just bottoms out and dies, as if I'd turned off the key. Restart it, throttle forward, dies. Restart it, throttle forward, dies. Maybe on the fifth repeat of this, it sputters and reluctantly comes out of the hole. Once it does run, it's fine. Until I stop again, then the whole thing repeats. It's maddening.
It gets worse as the day goes on, so by the time I'm trailering the boat and puttering around the dock and ramp, the idle is so bad that to move I have to nudge the throttle, then QUICK throw it in neutral and raise the idle throttle to keep it from stalling.
OK, this is what I've done to try and fix it. My untrained brain thinks it's a fuel system problem, so I attacked that. I replaced all the fuel lines, fittings and primer bulb. I rebuilt the fuel pump twice. I've done the SEAFOAM treatment several times. Twice I've taken out the carbs, soaked them, and followed my SELOC book's carb service procedure. I replaced both inlet needles. I DID NOT replace the floats, because I could not find new ones. I have no idea what bad floats look like, but these guys are orange plastic with a rough surface. Spark plugs are brand new. Did a compression test and all was OK there. I've fiddled with the idle/mix screws, backing them out various distances from lightly seated. Nothing seems to help.
"The Problem" will not go away and it's making me so frustrated. Questions: how can the motor run so well when it's cold then so miserably once it's warmed up? Am I on the right track by believing it's a fuel delivery problem? Should I replace the carb floats (if I can find some new ones somewhere)?
Thank you for reading this and I would LOVE some input or ideas.
It's a Mercury 75HP from 1986. Serial number is 0A984714. Cold start is fine. Couple of gas bulb pumps and she fires up and idles nicely. Sits and purrs while I put my truck away, etc. Then, for the first hour, everything is awesome! She jumps out of the hole. Drops down to No Wake speed under bridges without a hiccup. Quick response to all throttle changes. Seriously, I couldn't be happier. Then, after I've stopped for the first time, to fish or swim or play with the kids, that's when "The Problem" begins.
Here's what I call "The Problem". After this motor has been running awhile, like I said, 45 minutes or an hour, restarting it is difficult. I have to pump the crap out of the fuel bulb, and crank it for some time before it starts. Much harder start than when it's cold. Idling is very low and rough, and I have to play with the idle throttle to keep it from stalling. During "The Problem", the motor dies when I push the throttle forward. Like, it just bottoms out and dies, as if I'd turned off the key. Restart it, throttle forward, dies. Restart it, throttle forward, dies. Maybe on the fifth repeat of this, it sputters and reluctantly comes out of the hole. Once it does run, it's fine. Until I stop again, then the whole thing repeats. It's maddening.
It gets worse as the day goes on, so by the time I'm trailering the boat and puttering around the dock and ramp, the idle is so bad that to move I have to nudge the throttle, then QUICK throw it in neutral and raise the idle throttle to keep it from stalling.
OK, this is what I've done to try and fix it. My untrained brain thinks it's a fuel system problem, so I attacked that. I replaced all the fuel lines, fittings and primer bulb. I rebuilt the fuel pump twice. I've done the SEAFOAM treatment several times. Twice I've taken out the carbs, soaked them, and followed my SELOC book's carb service procedure. I replaced both inlet needles. I DID NOT replace the floats, because I could not find new ones. I have no idea what bad floats look like, but these guys are orange plastic with a rough surface. Spark plugs are brand new. Did a compression test and all was OK there. I've fiddled with the idle/mix screws, backing them out various distances from lightly seated. Nothing seems to help.
"The Problem" will not go away and it's making me so frustrated. Questions: how can the motor run so well when it's cold then so miserably once it's warmed up? Am I on the right track by believing it's a fuel delivery problem? Should I replace the carb floats (if I can find some new ones somewhere)?
Thank you for reading this and I would LOVE some input or ideas.
