Mercury 25XD - Trouble keeping it running

Base.v5

Cadet
Joined
Jan 20, 2012
Messages
11
I have a 1984 Mercury 25XD, serial #6453715. I purchased the motor last year with a jon boat. Let me state that this is my first boat & motor.

I had it on the water twice and it ran fine (as far as I know of boat motors). The third and last time on the water, it started dying when opening up to full throttle. Finally figured out we could run back to the dock as long as we didn't open it up. The motor has sat the last several months awaiting the time and weather to work on it.

First thing I did was order a manual, a dvd, and read tons of forum posts about boat motors. I had a friend get me a carb kit since I believed this was a fuel issue. I rebuilt and cleaned out the carb and attempted to restart the motor. I could not get it to stay running for anything. I then replaced the fuel line from the filter to the carb to see what the gas was doing. When I tried to start it the fuel line would be sucked dry and not pull any more gas. When shut off, air would rush from the carb into this line. I figured the pump/ant-siphon had gone bad so I got another one. I replaced the old pump line and the fuel lines in the motor. The motor will now start and run for varying lengths of time (much better than before).

The issue now is that it still seems to be starving for gas. Sometimes it runs great at idle, other times it will die when I push the choke back in. Several times it will run well enough to put into gear and open it some, but it will die as soon as I return it to the neutral position.

Where do I go from here? What should I check next?

I also noticed today while looking over the engine that there seems to be a bolt missing... What is this and would it have any effect on the engine's performance?

missingbolt.JPG

Thanks for any help or info. These forums have been a great source for me trying to learn how my engine works and how to fix it!
 

jbjennings

Captain
Joined
Jul 18, 2007
Messages
3,903
Re: Mercury 25XD - Trouble keeping it running

The missing bolt just holds the exhaust cover on. There's a possibility that there is a sheared off bolt in the bottom of the hole---hopefully not. It needs to be replaced but probably is not the problem unless it is not holding the cover on tight and water is spraying into the exhaust ports. If water is spraying on the exhaust ports, you would likely see milky stuff on the spark plugs after running it, or the plugs would be extremely clean due to getting steam cleaned.
I would pull the fuel line off the carb and pull it over a couple of times to see if you're getting a good pulse of fuel from the fuel pump to the carb. If so, reclean the carb, making especially sure that your float needle has no grit on it and the float is parralel to the top of the float bowl when upside down.
Good luck,
JBJ
 

Base.v5

Cadet
Joined
Jan 20, 2012
Messages
11
Re: Mercury 25XD - Trouble keeping it running

I've ordered a few more parts that didn't come in the carb rebuild kit that I want to replace, including a new inlet needle. I will open up the carb to replace the parts and see if I missed anything the first time around.

The fuel pump is integral to the carburetor. The only fuel lines are to the fuel filter and from the filter to the carb/pump. Maybe I didn't get the seals on exactly right, so I'll check that as well.

Any chance this could be a timing or sparking issue? Or should I just focus on the fuel delivery?
 

jbjennings

Captain
Joined
Jul 18, 2007
Messages
3,903
Re: Mercury 25XD - Trouble keeping it running

Checking for spark on both cylinders is such an easy task with a $6 spark tester from autozone, that I would definitely do it. Weak spark on one cylinder can definitely mimic a carb problem. However, since you are having it die when pushing in the choke.......Well, that's a classic symptom of a dirty carb or fuel restriction.
JBJ
 

Base.v5

Cadet
Joined
Jan 20, 2012
Messages
11
Re: Mercury 25XD - Trouble keeping it running

How long can you run a motor hooked up to muffs? Is it OK to open it up or should I wait until I get on the water to run it full out? I don't want screw this thing up any more than it already is!

Thanks for any info.
 

jbjennings

Captain
Joined
Jul 18, 2007
Messages
3,903
Re: Mercury 25XD - Trouble keeping it running

You can run it all day on muffs if you want to as long as you're getting good water flow.
However, under no circumstances do you give it any throttle on muffs. If you try to put it in gear and run it fast, the lack of back pressure on the exhaust and lack of resistance on the prop will cause it to overrev and you may throw a rod.
Good luck,
JBJ
 

Base.v5

Cadet
Joined
Jan 20, 2012
Messages
11
Re: Mercury 25XD - Trouble keeping it running

Thanks JBJ, you may have saved me from ruining the motor.

So I got the parts in and opened up the carb again... and I noticed I had put two of the seals on in the wrong order :redface:

I replaced the parts and got the seals back on and put it all back together. It stays running now, but only when I leave the choke out. If I push it in, the engine dies pretty quickly. If I pull the choke back out quickly it will rev back up. Playing around with some adjustments, I think I may have to fine tune the idle mixture screw. Any other suggestions?

I have two more questions.

Is this normal? It is frothy oil coming out from inside the prop when I run the engine.
propoil.jpg

Also, I have a WMC carb on the motor. Is there a one way valve between the diaphram and the fuel bowl? While trying to make sure all the jets/ports were clean, I noticed what looks like a metal flap or something there. What is this?
 

Base.v5

Cadet
Joined
Jan 20, 2012
Messages
11
Re: Mercury 25XD - Trouble keeping it running

Any thoughts on the oil in the prop? It's not a lot that comes out, is this normal?
 

oldman570

Lieutenant Commander
Joined
Mar 25, 2011
Messages
1,615
Re: Mercury 25XD - Trouble keeping it running

Yes oil comming from the prop is normal when run on muffs as that is the ehuast from the motor running and oil that is not burned during combustion. When rebuilding the carb it has to be taken completly apart and ALL jets tubes cleaned and blowed out with air to make sure that everything is clean. The metal valve in the pump section has to be placed in the right direction inorder for the pump to work correctly as it is a check valve.The low speed jet needs to be screwed in lightly to the seat then backed out 1 1/4 turns for startup ,then adjusted from there after motor has warmed up. Idle needs to be set at 600 to700 RPM with warm motor in water and in gear.
 

Base.v5

Cadet
Joined
Jan 20, 2012
Messages
11
Re: Mercury 25XD - Trouble keeping it running

Good information oldman. Thanks for the clarifications.
 
Top