1998 Mercury 225 Offshore, Low RPMS at WOT, then eventually increases...

bbbailey

Recruit
Joined
Dec 3, 2012
Messages
2
Bought a boat with 1998 Mercury 225 HP outboard offshore series. Used from dealer. Took boat on test drive, would not get above 300 rpms. They had their mechanics look at it, called me a week later and said oil unit had failed and they could either disconnect or replace. They disconnected when I told them I was okay with that. Test drove boat, performed great! Here where fun starts. Get boat home, go out of town for thanksgiving, so boat sits a week or so without being used. I get back, put boat in water, and low and behold it will not go over 300rpms at WOT. In neutral will rev higher. Pulled out of water and put on hose, ran higher rpms. Next day, put it back in water, 300 rpms at wot and about 8 mph. I trimmed all the way down with motor, all down on trim tabs. After a couple of minutes I notice motor picking up a little on rpms and speed. Then gradually over next couple of minutes the motor runs out as one would expect it to. Motor will run at 3/4 to WOT normally as long as you want to run it after that, However, if you ever slow down, stop, etc., the whole ramp up process starts over.
I am using non ethanol fuel that is fresh and mixed new quicksliver at 50:1
The shop I bought boat from cleaned all injectors and new plugs before disconnecting oil sending unit.
Could this be a problem with oil unit not being correctly disconnected? Fuel problem/delivery? Plug wires? Any ideas or help would be greatly appreciated.
 

bbbailey

Recruit
Joined
Dec 3, 2012
Messages
2
Re: 1998 Mercury 225 Offshore, Low RPMS at WOT, then eventually increases...

3000 rpms, not 300
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,589
Re: 1998 Mercury 225 Offshore, Low RPMS at WOT, then eventually increases...

Carbs dirty , sync and link off or slipped, fuel pump weak or failed CDM modules as the 1997-98 had problems with this.
 
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