Help with outboard; Merc 25hp

[SylvanOwner]

I have an early 80's Mercury 25h.p. outboard that has a problem with bogging down/out. It has been doing this for a few seasons now but is getting worse. It starts OK and idles fine and accelerates fine but after running WOT for a while it just loses RPM (and power obviously) and will drop back almost to an idle. It will sometimes stall and be difficult to start again (although it always does) but usually just runs low for a bit and you can accelerate partially and usually find a point around 1/4-1/3 throttle where it is happy and will sometimes let you go to WOT again but after a while will drop back. I'm spending less and less time at WOT and it sucks. It first started when the boat (14' tinny) was under most load - hauling camping gear and guys - but now happens, well, all the time.

I CAN keep it at WOT by pumping the ball every few seconds so it seems to be a fuel supply issue.

I've changed plugs, cleaned plugs, changed the fuel line, used carb cleaner and gas line antifreeze, cleaned the filter. What about this magic SeaFoam stuff? Where to buy in the GTA, ideally somewhere between south Etobicoke and BassPro?

Any suggestions as to what may be the issue would be most appreciated.

[Fisherman]

I have an early 80's Mercury 25h.p. outboard that has a problem with bogging down/out. It has been doing this for a few seasons now but is getting worse. It starts OK and idles fine and accelerates fine but after running WOT for a while it just loses RPM (and power obviously) and will drop back almost to an idle. It will sometimes stall and be difficult to start again (although it always does) but usually just runs low for a bit and you can accelerate partially and usually find a point around 1/4-1/3 throttle where it is happy and will sometimes let you go to WOT again but after a while will drop back. I'm spending less and less time at WOT and it sucks. It first started when the boat (14' tinny) was under most load - hauling camping gear and guys - but now happens, well, all the time.

I CAN keep it at WOT by pumping the ball every few seconds so it seems to be a fuel supply issue.

I've changed plugs, cleaned plugs, changed the fuel line, used carb cleaner and gas line antifreeze, cleaned the filter. What about this magic SeaFoam stuff? Where to buy in the GTA, ideally somewhere between south Etobicoke and BassPro?

Any suggestions as to what may be the issue would be most appreciated.

 

By your diagnosis of "pumping the primer bulb and it will keep going", you have a fuel delivery problem, anywhere between the tank and carb. It could be as small as the "O" rings onn the connectors if those models have them, a small crack in the fuel line or a loose hose clamp.

[SylvanOwner]

By your diagnosis of "pumping the primer bulb and it will keep going", you have a fuel delivery problem, anywhere between the tank and carb. It could be as small as the "O" rings onn the connectors if those models have them, a small crack in the fuel line or a loose hose clamp.

 

 

Thanks Fisherman for the quick reply. Forgive my ignorance I'm no small engine mechanic - "o" rings on what connectors? How do I check this? Have changed the fuel line and experienced same problem, will double-check the clamps but don't think that's the problem as it would've been covered when the line was replaced.

 

 

Should also just say for anyone who else who may try and help that I DO have the vent open on the tank.....just sayin'.

 

Dan

[rpsmith]

Did you replace the gas tank as well? Had the same problem myself and fixed by buying a new gas tank. The connection at the tank was the problem. Also check the gas line connection at your engine.

[SylvanOwner]

Did you replace the gas tank as well? Had the same problem myself and fixed by buying a new gas tank. The connection at the tank was the problem. Also check the gas line connection at your engine.

 

 

I haven't replaced the tank but did clean it out. There was some crap floating around on the bottom which I was able to wash out and then thoroughly dry the inside. Also used gas line antifreeze after doing this to ensure no moisture in the system. Thanks for the reply.

 

Dan

[Fisherman]

The "O" rings I mentioned are found on the inside of the connectors at both the tank and engine ends, did the new hose come with new end connectors? If you used the old connectors, check. There's also the possibility that you have a bunch of floating crud inside the carb and it's jamming the fuel passages. It may need a thorough cleaning. Seafoam can be found at most NAPA or Carquest stores. Good luck

[Fish4Eyes]

check PM

[Rattletrap2]

Check inside the fuel tank. Look at the fuel pick-up tube. On the bottom, they sometimes have a screen attached to the bottom of the tube to pre-filter any debris. On mine, the screen adaptor ended up getting slid too far onto the hose and the open end of the poly tube was actually bottomed out against the end of the adaptor. This only allowed a partial restricted flow of fuel to the hose connector on the tank. My 20 H.P Merc would run fine at low speeds, but bog down and cut out if I tried to go WOT. Slide the screen off the hose a bit and secure it with a tyrap.

 

Good luck!

[jimmer]

You might have to take the carb right off and do a thorough cleaning. Seafoam is good to a certain degree, but it has its limitation. Sounds like a lot of crap building up in the carb.

I just went through the same thing on my 25 yamaha and seafoam helped after running a tank with seafoam though it. But who really knows, it could have been a bad tank of gas or water in the fuel also. All the suggestions are important to look into. Sucking air could cause the problem, but you should see some gas leaking somewhere if that was happening. You also said you replaced the hose with a new one, so you have eliminated one possible source of the problem.

Also try to use fuel stabilizer in all your fuel if it is going to sit for awhile.

[misfish]

Like the last thread,sticking needle valve.HAD THE SAME MOTOR SAME PROBLEM.Pump and she goes,stop pumping and blaaaaaaaa.

[WeedLine]

Hey Dan, been a while. I have a tank, fuel line, connectors and 3/4 of a can of Seafoam. You can have all of it. Give me a call.

[Nipfisher]

We had a 1986 Merc 25 and it was the WORST motor ever. We would start it in the driveway before each trip then travel to the launch only to have it refuse to start. It was at the mechanics several times and always cost $60-$100 each time we had it in.

 

On a freaky note...we were wayyyyyy back in a remote bay on Lake Temagami and as we landed at our camp site we noticed smoke coming from under the cowling. As I lifted it off the entire electrical area on the right hand side of the motor was on fire. I disconnected the gas and threw it to the front of the boat. Then I jumped out into the shallow water and began splashing the motor. When it was done and cool I hooked up the gas and it fired right up. Even though all the wires were melted together it seemed to work o.k. We got it all re-wired when we got home.

[SylvanOwner]

Hey Dan, been a while. I have a tank, fuel line, connectors and 3/4 of a can of Seafoam. You can have all of it. Give me a call.

 

 

Hey Bud, thanks for the offer, I'll give you a shout later today.

 

 

Thanks to everyone for all the feedback so far, had a PM or 2 as well. Will explore some options Saturday and try to take it out for some exercise Sunday - report back next week.

 

Dan

[Krisco]

Hey Bud, thanks for the offer, I'll give you a shout later today.

 

 

Thanks to everyone for all the feedback so far, had a PM or 2 as well. Will explore some options Saturday and try to take it out for some exercise Sunday - report back next week.

 

Dan

 

Hey guys,

 

I have an also similiar problem with my 2002 25 hp Merc. It loses power at WOT for a split second the it jumps right back. I have been through all the fuel system trouble shooting with little success. This motor sits in my garage all year and I only use it 2-3 weeks out of the summer up north. I believe it can't have more then 50 - 70 hrs of run time in its life. I ran it for a week in June and it ran great. Last week I went back up north and started having problems.

 

I took it in to a marine mechanic this week thinking all it needed was a carb clean out and so did he. Well he called me yesterday and told me he did a compression test on it and got 110 psi out of one cylinder and 92 on the other. Under further investigation he stated that the wall of the lower compression cyl had a score in it, not sure of the root cause.

 

So, to make a long story short he told me it would only be a matter of time before I through a piston. I asked him for alternatives and he told me he does have a used 25 Evinrude 4ST he would sell me. he told me he would give me $ 600 on a trade.

 

What do you guys think? he is a reputable mechanic. I was not planning on buying another motor. Should I tell him to put it back together for me and take my changes?

 

Is it possible to run low compression in the 1 cylinder? I am heading north again in 2 weeks and do not want to be rushed into finding another motor in a hurry, like to take my time with these purchases.

 

Sorry, I was not trying to hi jack this threat, just looking for some input.

 

Thanks

[Randy Barrett]

I have an early 80's Mercury 25h.p. outboard that has a problem with bogging down/out. It has been doing this for a few seasons now but is getting worse. It starts OK and idles fine and accelerates fine but after running WOT for a while it just loses RPM (and power obviously) and will drop back almost to an idle. It will sometimes stall and be difficult to start again (although it always does) but usually just runs low for a bit and you can accelerate partially and usually find a point around 1/4-1/3 throttle where it is happy and will sometimes let you go to WOT again but after a while will drop back. I'm spending less and less time at WOT and it sucks. It first started when the boat (14' tinny) was under most load - hauling camping gear and guys - but now happens, well, all the time.

I CAN keep it at WOT by pumping the ball every few seconds so it seems to be a fuel supply issue.

I've changed plugs, cleaned plugs, changed the fuel line, used carb cleaner and gas line antifreeze, cleaned the filter. What about this magic SeaFoam stuff? Where to buy in the GTA, ideally somewhere between south Etobicoke and BassPro?

Any suggestions as to what may be the issue would be most appreciated.

 

Just because the vent is open doesn't mean it is working.

 

Next time out run it till it starts to lose power, once this starts,loosen the gas cap and see if it clears up. Sounds like a vent problem and the tank is going to a vacuum pressure preventing proper fuel supply. Once you are back at an idle it allows the vacuum presure to release allowing it to run better again until you increase fuel demand again.

Edited July 24, 2010 by Randy Barrett

[Big Cliff]

You mentioned you "cleaned the fuel filter" try replacing it before you do anything else. let me know how that works for you.