25 HP Mercury Problems

Sea Foam · 02-06-2009, 05:44 AM

Help! Last year I started heving problems with power on A 2005 25 hp Mercury. It had been running fine and then suddenly it wouldn't put my 15" Sylvan into a plane. I took it into the people I bought it from and they couldn't find anything wrong with it and said that it hits 5,000 rpms with no problems. Took it out and had the same issue. Went back to them and this time they said to try a new tank and line. Did that and still no power. Anybody had this kind of a problem before. Oh yeah and I changed plugs after the first time it started acting up So I don't think thats it.

sschwab · 02-06-2009, 07:07 AM

Did you change anything on the boat or motor? Is there more weight on the boat? Did you change the trim? Prop? Fuel?

Just some questions to start with...

Sea Foam · 02-06-2009, 11:56 AM

Haven't changed anything except the tank and line and that was after talking to the folks at the dealership

raptorschild · 02-06-2009, 12:47 PM

I'm not mechanic, but could there be an issue at the prop connection.

Bloom · 02-06-2009, 12:56 PM

It could be any number of things, including low compression, vacuum leak, fuel starvation, retarded spark. I'm placing my bet on fuel starvation. The dealer may have run it up statically, but unless it's under a load, that won't tell you much. I would start with inspecting the fuel line, connections, bulb, etc. and then drain the carb, remove the bowl and see what kind of crud is in there. It could be a partially clogged main jet, in which case, it's best to pull it down and rebuild.

Just-in-Time · 02-06-2009, 02:43 PM

you need to find out what rpm's she hits

Lou · 02-07-2009, 07:22 AM

Quote:

Originally Posted by Bloom

It could be any number of things, including low compression, vacuum leak, fuel starvation, retarded spark. I'm placing my bet on fuel starvation. The dealer may have run it up statically, but unless it's under a load, that won't tell you much. I would start with inspecting the fuel line, connections, bulb, etc. and then drain the carb, remove the bowl and see what kind of crud is in there. It could be a partially clogged main jet, in which case, it's best to pull it down and rebuild.

Yes you must check it under load.
Could the trim adjustment have changed?
Fuel starvation would be the place to start.
Does the RPM's change when you sqeeze the bulb?
It really needs to have some kinda of load.
Let us know

Sea Foam · 02-10-2009, 04:43 PM

I'll have it out here again the first of next month and I'll try it with the cover off. I was thinking fuel starvation recently and gave the bulb several squeezes when I had it had it out last. No change.

GregE · 02-12-2009, 04:04 PM

Had a similar problem caused by a weather cracked bulb. Ran fine at idle but sucked air at load. Took me two trips to figure it out.

Lou · 02-13-2009, 10:20 AM

Quote:

Originally Posted by GregE

Had a similar problem caused by a weather cracked bulb. Ran fine at idle but sucked air at load. Took me two trips to figure it out.

And when it's cold. When you 'changed every thing' did change the bulb?

shinook65 · 02-13-2009, 11:32 AM

Is it a 4stroke ? Its the valves!! My buddy had the same problem on his 25 hp bigfoot.. Took it to a shop, they said carb. Ordered new carb, took it to the river, same problem. Took it back, shop said new carb was faulty. Ordered second new carb.. Two weeks later picked boat back up.. (Keep in mind,boat ran like a top not under load) launched boat, same problem!! Finally boat mech threw in the towell and referred him to Marks Mercs in Salem. Marc asks, have you adjusted the valves? Ummmm no... He said pick it up tomorrow.. Picked it up, launched it, and ran up and down the river at 22 mph...

Have the valves adjusted..

Closepin · 02-13-2009, 08:04 PM

i'm assuming it has a prop on it and not a pump??

FISHSTALKER03 · 02-14-2009, 03:46 PM

I have a 2003. I would get up and go and after a time would start to smoke and lose power. It would idle for a while and then be fine. I got it home and it was almost out of oil. Took it to the dealer. They put it in the tank and ran it and said it's fine. I took it out again and had the same problem. Finally I went on line and started asking questions like you are doing. One fellow back east responded. He stated Mercury had installed the wrong power head gaskets in a lot of these motors. The fact is that Mercury kept quiet and didn't send out any notification. I made my dealer call in to the factory. He was advised that this was the case. A week later the problem was solved. It was all covered under warranty.
This may or may not be the problem with yours but this is the fourth time I have posted this info on different forums.
Good Luck>

GregE · 07-18-2011, 01:24 PM

Good info
Bump for future reference