Help on engine

[stuartsx5]

I have a 97 Force by Mercury.  I have no problems with it till a couple weeks ago.  My wife and I were out for a ride and we were at full throttle, right at 5,000 and it just seemed like it lost power and dropped to around 4,600 and sounded like it was bogged down.  We were low on gas the first time it happened but I have added gas and it didn't help.  I use the Stabil for marine in it every time I fill up.   Now it won't get over the 4,600 rpm and sounds bogged down all the time.  I hav e checked for water in the gas, the fuel filter, and pulled the plugs.  I don't know what a fouled plug looks like so I uploaded pictures.  Should I be looking at fuel issues? Air issues?  Is there a screen in or filter in the tank that could be plugged?  It runs smooth at the higher rpm and I haven't noticed anything different at idle either.  Thanks in advance for any advice.

[fishinwrench]

Need to have a compression test, then an ignition output test.  If both of those elements check fine then it is a fuel system or cooling system problem. 

What size outboard is it ? (2 cyl., 3cyl., 4 cyl., or 5 cyl.?)

[stuartsx5]

Thanks wrench. It is a 4 cylinder 120 horse. I can do the compression check but have never done the ignition output test. Is that something I can do myself? Would it drop like that if it quit sucking up water? I still have water coming out of the telltale. 

[fishinwrench]

To test the ignition system you'll need a digital voltmeter with a peak reading adapter (DVA), and some good instructions specific to the system (which I can provide if you get your hands on the voltmeter and adapter).     The charging system (stator and voltage rectifier/regulator) can cause the symptoms you describe and it can be tested with any old voltmeter (digital or analog).

The cooling system can cause a loss of RPM even if sufficient water pressure appears to be coming from the pee hole or is indicated on a water pressure guage. 

But first things first....Check compression, because nothing else matters until you verify that.

[stuartsx5]

Thanks Wrench.  I did the compression test just now.  I did it the first time just by taking one spark plug out at a time and testing the cylinder with the others still in and I hit the starter 3 times on each cylinder.  Each cylinder tested between 120 and 125.  Then I read the instructions and it said to take all the spark plugs out and test so I did that and only hit the starter once on each cylinder.  I got 89 to 95 on all but one cylinder and it showed a little over 100.  Do these sound good?  I know they should all be in the same range but I don't know if that is the numbers we are looking for.  One of our company mechanics just transferred into my department and he says he has what I need to do the tests you are talking about but I would still need instructions cause he doesn't know anything about outboards. Thanks for your help, I decided to go back to school for some crazy reason and this is finals week.  If it takes me a while to respond please don't think I am ignoring your advice, I'm just writing papers.....

[fishinwrench]

Missed this, sorry.   

Those compression numbers aren't too good.  Sounds like it's probably got some ring sticking going on

[stuartsx5]

No problem. It is beyond my skills so I took it to Fair Grove Marine over the weekend and he said he will take a look at it this week. Thanks for your help.