25hp 4 stroke mercury idles great loss of power/rough

[Wilsonriverfisher]

I posted this before but i did not reallly describe the problems to the best of my ability maybe a little more detail will help. I bought this motor recently USED so i dont know the history on it. Ive taken it out several times with no problems it got up on plane fast each time out. The last time I took it out I started it up and took off and after about 1 imute or so I could notice a lack of power like something was holding it back also it seemed a little rougher than normal while giving it power. I throttled down and then the alarm came on beep...beep...beep so I did what I thought i needed to do and shut it off and waited a second....I then started it back up and proceded to go back to the dock slowly almost at idal. I went home and took the plugs out and checked the oil it was low but nothing serious so I thought the low oil might have triggered a rpm reduction and caused the alarm to go off. I changed the oil and took it back out and it started and ran nice very smooth idal. I thought maybe it was cool then i took of to get on plane and it still sounded rough and sluggish a severe lack of power. at idal i checked for a pee stream and it was peeing good. I have ordered a manual and am waiting shipping. I was hoping maybe somebody has experienced these syptoms or can help me with questions this is my first time repairing a outboard

 

[Wilsonriverfisher]

Re: 25hp 4 stroke mercury idles great loss of power/rough

***Update***

I checked and tested the thermostat it opens around 140 and closes in cold water. Also checked the spark and that seems good, compressions shows 110 both cyclinders, I might take the carb off and rebuild it? Tested the pump in water tank and it pups water good

 

[drew]

Re: 25hp 4 stroke mercury idles great loss of power/rough

What model? Is this a Yamaha powered Bigfoot? The beeping is low oil pressure or overheating.

***Update***

I checked and tested the thermostat it opens around 140 and closes in cold water. Also checked the spark and that seems good, compressions shows 110 both cyclinders, I might take the carb off and rebuild it? Tested the pump in water tank and it pups water good

 

[Wilsonriverfisher]

Re: 25hp 4 stroke mercury idles great loss of power/rough

problem is still there Compression is good, thermostat opens at 140 changed the impellar. Im lost

 

[totallyconfused75]

Re: 25hp 4 stroke mercury idles great loss of power/rough

What year model is your motor? I have a 2007 merc. 25hp 4 stroke with a stainless steel prop. Last year it seemed to have a much better hole shot than this year. It still wasn't that of a 2 stroke, but it wasn't bad (ss prop helped some). This year, I also added a breakaway unit to allow the motor to "kick up" when it hits something (lot of duck hunting on rivers). The motor runs and idles just fine, it just doesn't seem to have the same power to get up on the water. Once it's up on plane, it runs great. I trim the motor up to level and it scoots across the water with no problem. Just can't seem to get out of the hole good!!

 

[jedma]

Re: 25hp 4 stroke mercury idles great loss of power/rough

i have a merc 25 hp 2003 had same problem couple years ago put new plugs in that seamed to fix it.

 

[HenryD]

Re: 25hp 4 stroke mercury idles great loss of power/rough

Hello,
I seem to have the same problem. The motor starts very easily. It runs at idle fine. When I try to advance the throttle, the motor does not have any power and it will stall if I try to go about 3000 RPM.
I have replaced fuel filter. I have replaced plugs. I am using new fuel in a separate can. I tried cleaning the carburator with Sea Foam Deep Creep and Sea Foam cleaner.
I know almost nothing about about outboards...
HELP!