Mercury 25 HP help

[jeepguy]

I have a mercury 25 hp that has recently developed a problem. I am in the process of diagnosing it and was wondering if anyone had any suggestions.

Here is the problem....

Motor starts fine, get going and it bogs down. It is as if it is being choked and eventually kills. I am going to add seafoam to the gas and hope it improves, I have also considered carb cleaner and new plugs.

Any thoughts or help would be apprediated.

[CAMAN]

1st check the gas tank vent and make sure it open and not plugged.

If that's good check all the fuel lines for cracks, punctures and obstructions. Depending on how old they are you may want to just go ahead and replace them all.

Also check the primer bulb and make sure it is flowing in the right direction and isn't crcked or punctured or has an obstruction.

[jeepguy]

Yeah, now that I think of it, when I prime it a little gas comes out of the line at the motor. It is the original 1987 tank and line assembely, I am going to go to fleet farm and get a new tank and lines.

[Eelpout08]

sounds to me like a clogged jet or passage in the carb or a fuel delivery problem- ie, bad pump,broken or leaking lines, etc.

[CAMAN]

Yup, good idea to replace it all if its 25 years old. Also replace whatever lines feed the carb and get a new (or clean it if its the basket type) fuel filter. Also replace the O-ring on the basket filter.

[jeepguy]

sounds to me like a clogged jet or passage in the carb or a fuel delivery problem- ie, bad pump,broken or leaking lines, etc.

Is this something I would need a mechanic to diagnose?

[CAMAN]

You said the motor starts and runs fine until you give it gas. I wouldn't mess with the carb until you have done the cheap and easy things first and narrowed it down a little more.

And yes, if you have never done a carb rebuild before, it may be best to bring it to a mechanic. Or get the repair manual for it if you feel up to the challenge, it will walk you through it.

[jeepguy]

Had the carb rebuilt and ignition coils replaced with the last 18 months.

[mn_bowhunter]

Mine would do the same thing. I replaced the fuel line from the primer up to the motor, and replaced the fuel filter o-ring. Motor runs great again. Air can get in if you are leaking fuel causing the motor to suck air and not fuel. The fuel filter check is easy. Take off the motor cover and check for leaks as you pressurize the primer bulb. Any leaks replace the part. My motor is one year newer, and the fuel filter o-ring is square shaped and only a couple bucks from a merc dealer. The screen filter is in the canister on the upper part of the motor if you trace the fuel line. If any of this is the problem it is very easy to fix yourself.

[jeepguy]

Thanks I a headed to Fleet Farm tomorrow to get a new line and to the merc dealer for the o-ring if it needs, I am checking after the baseball game.

[marine_man]

Had the carb rebuilt and ignition coils replaced with the last 18 months.

Has the motor sat much during the season this year, without stabilized gas?

marine_man

[jeepguy]

It sat most of the summer, last itme used was 4th of july, so yes.

[marine_man]

I would address all the easy stuff you can do, as mentioned above. But, I wouldn't be surprised if your gas has varnished up the carb a bit and you have a piece of crud blocking the high speed jet.

marine_man

[boatfixer]

I would address all the easy stuff you can do, as mentioned above. But, I wouldn't be surprised if your gas has varnished up the carb a bit and you have a piece of crud blocking the high speed jet.

marine_man

I concur

[jeepguy]

Will a little seafoam in the gas and/or carb cleaner sprayed on the carb do the trick?

[marine_man]

Nope... if all the easy external stuff doesn't work you'll need to remove the carb from the motor, take it apart and clean out all the passages.

In the future, if you suspect the motor will be sitting for more than a couple of weeks, be sure to run fuel stabilizer through the motor prior to leaving it sit. It should help you avoid issues like this.

marine_man

[delmuts]

"In the future, if you suspect the motor will be sitting for more than a couple of weeks, be sure to run fuel stabilizer through the motor prior to leaving it sit. It should help you avoid issues like this."

Or! As instructed by my mechanic after he got done cleaning the nasty gunk out of the carbs of a boat i had just bought. Run sea foam in the gas all the time. Stabilizes the fuel and helps clean the carbs too.

[marine_man]

Yep, that works too, Del!

marine_man

[311Hemi]

Yeah, now that I think of it, when I prime it a little gas comes out of the line at the motor. It is the original 1987 tank and line assembely, I am going to go to fleet farm and get a new tank and lines.

I suspect all new lines should resolve the issue if it's leaking when primed. We had the same issue with out 85' 20hp Merc.

If you have not yet replaced it (as mentioned) get a new fuel filter and o-ring. It's very simple to change and will only take a couple min. Also inspect the fuel lines going to and from the fuel filter for any cracks/leaks.

[FM_Mike]

One other thing to check is the fuel line that goes in the tank itself. Had that problems may years back. The line in the tank had rotted off only allowing gas to the carbs when the tank was completely full. And easy fix if that happens to be the issue. If you have access to a different tank or want to pull the fuel level indicator and check.

Just a thought.

Mike

[jeepguy]

Today I out her in the water and tried to start it up. Well now it will not start for more then a second. Well when I prime the motor the basket fuel filter does not fill and the primer ball nefver gets hard. I wonder if this means I need to replace the fuel line or the diaphram style fuel pump. WHEN I SQUEEZE THE BALL IT SOUNDS LIKE AIR IS THE ONLY THING MOVING THROUGH THE LINE.

[patsrock]

I have not checked the whole thread , but make sure the bulb is pointing up. Arrow up , it does make a difference in the bulb firming up.

[marine_man]

It sounds like your primer bulb is shot, or you have a hole in you fuel line between the gas in the tank and the primer bulb.

What you can do is unhook the fuel connector fitting on the hose and push something against the little ball in the connector and squeeze the primer bulb. If you're not getting gas coming out the end it's definitely a air leak.

marine_man

[jeepguy]

I have norrowed down my problem on my mercury 25 HP motor to being a matter of fuel not being delivered. I can pump the primer bulb till the cows come home and it never firms up, nor does the basket type fuel filter fill up barely at all. I am starting by inspecting the fuel line, probably replacing it, then looking to see if the fuel pump diagphram is ruptered. Any advice on what else it could be.

[jeffreyd]

fuel line or dip tube in the tank could be broken or leaking.