25horse mercury?

[Tyler23]

i have a mercury 25 made around the early 90's not exactly sure. i ran it all season last year for duck hunting and it seems to run fine(except it likes to smoke) but once i get to full throttle and bogs out? i went threw the motor carbs, reed valves, compression, fuel mixture, plugs and it still didnt fix the problem. any ideas?

[boatfixer]

Is it dying or just bogging down losing power? Did you completely clean the carburator? Double check all the fuel line connections to start. How about the filter? did you change that too? My first inclination is that it is starving for fuel.

[Tyler23]

it just like bogs out and looses power but if i let of a bit it will take off again? well i went threw the carb at first and then it still didnt fix it. so i took the whole carb down to the local shop and they went threw it and said everything looks good. i never looked at the filter? but all the lines are new.

[marine_man]

If you pull the choke when it bogs out does it pick up?

marine_man

[LindellProStaf]

Fuel pump. Mine did that too. I have a 50 Merc. Cleaning the carbs helped a little but not completely. I got a fuel pump kit. Worked great. I did it on the kitchen table so I would not drop anything. Just make sure all of the diaphragms go back in the right order. Good luck.

[Tyler23]

i couldnt tell you i never tried that i just let off a bit and then it ran fine just not as fast. is this a fuel pump problem?

[marine_man]

It could be, but I wouldn't start replacing parts until you can identify that for sure.

It could be an air leak in the fuel line, water in the gas, coil cutting out at high speed, carb blockage...

marine_man

[Tyler23]

ok well all the lines have been replaced, fuel take, carb has been gone completely threw, reed valves good, new plugs. what should i look at first?

[311Hemi]

All fuel lines have been replaced, even the tank/engine lines?

If that 25 is similar to the mid 80's ones, they have a fuel filter that it between the carb and the gas line connection on the front of the engine. Have you replaced that filter and the 0-ring inside of it?

[boatfixer]

To isolate the fuel pump, have someone pump on the primer bulb when this is happening, if it picks up, theres your answer. The upside of rebuilding the fuel pump is it would be done and over with and diaphram kits are relativly inexpensive. Since you have not replaced the fuel filter yet, I would also consider doing that as well. Since it wants to pick back up when you let up on the throttle, thats again suggests that it is starving for fuel. Hitting the choke like MM said will also give some indication.

The ignition system has a low and high speed stator. They can run perfect at lower speeds and pretty much nothing above 2000 rpm if the high speed side has an open circuit in the windings. Following some of the advice given here, you should be able to determine if this is fuel or ignition. Checking the fuel system is much easier and than chasing down an ignition problem, which would be the main reason to help you determine which direction to go.

[Tyler23]

ok so ALL the lines have been replaced. i never monkeyed around with the pump or filter. i was hoping just to be able to narrow it down to a couple things and try them which boatfixer did say. hopefully soon enough the river by my house will be open enough to run it wide open and try pumping the bulb. so if that doesnt fix it im looking at some with the high speed stator? are those expensive?

[Tyler23]

i called down to the local marine shop and of corse they want me just to bring it down to them and im not going to do that unless i really have to.

[boatfixer]

They (stators) are, thats why we want to figure between fuel and ignition. Lets verify the fuel system is ok first.

[Tyler23]

i really hope its just the fuel pump because i can rebuild it for pretty cheap and i dont have to hunt down stupid electrical problems

[Grainbelter]

Had the same problem with my 25 merc, turns out I got lucky and it was the gas!! I would get up on plane full throttle and then it would just die, restart and repeat. Messed around a bit checking everything and everything looked good as with yours. Poured out the gas, went and got some new stuff and has run fine ever since. Also with an old 15 merc, I had a similar problem that turned out to be the fuel line from the tank to the engine, same symptons as well. Good luck.